Geology and Metallogeny of Copper Deposits

The symposium on copper deposits and the publication of its Proceedings are a good example of international scientific cooperation. The extensive exchange of opinions between specialists in different types of copper deposits has provided important new data on their geological setting and condition of formation.

The South Kawishiwi intrusion in the northern part of the Duluth Complex, Minn. is divisable into a sulfide-tree upper zone and a sulfide-bearing lower zone. The sulfide-free zone is mostly troctolite containing laterally persistent anorthosite layers. Sequences of troctolite and anorthosite form cyclic units in which the crystallization of plagioclase was followed by precipitation of plagioclase plus olivine. Chemical variations associated with cycles show trends either similar to or reversed from those expected under normal conditions of fractional crystallization. These trends, and the absence of any systematic chemical evolution, indicate that crystallization of the sulfide-free rocks occurred in a chamber that was continuously replenished by compositionally similar liquids. In contrast, the sulfide-bearing zone consists of a heterogeneous mixture of troctolite, picrite, dunite, anorthosite, oxide cumulates, and hornfels in which sulfides are ubiquitously disseminated. The sulfide-bearing zone has no discernible internal stratigraphy. The contact with the sulfide-free zone is sharp.The sulfides are predominantly pyrrhotiie, chalcopyrite with cubanite, and pentlandite occurring mostly as interstitial and included grains. The close association of sulfides with hydrous phases or with grains that show reverse compositional zoning indicates that volatiles derived from adjacent metasedimentary inclusions were important in sulfide formation. The wide dispersion of sulfides, heterogeneous mix of rock types, and absence of traceable units indicates that the rocks accumulated in an extremely dynamic environment that is thought to have been associated with rifting in this area. Faults presumed to be rift-related were active throughout the emplacement of this intrusion and, in part, control the distribution of the sulfide-bearing zone and the overlying rocks.

Analyses of the isotopic composition of S, C, O, and H in mafic igneous rocks may provide valuable information regarding the extent of contamination by continental crust material. Partial melting and devolatilization of country rocks are important processes in the generation of many Cu—Ni deposits associated with mafic igneous rocks. Sulfur isotopes provide a means of evaluating the possibility of extraneous sulfur addition to a melt. Variability and distribution of δ34S values may also provide data relating to the timing and mechanisms of sulfur production and incorporation into the melt. Oxygen, hydrogen, and carbon isotopes also can be sensitive indicators of isotopic contamination, whether by partial melting, devolatilization, or solid state exchange. Zones of contamination within an igneous sequence are likely to be areas where factors that control sulfide solubility (T, fS₂, fO₂, melt composition) have been perturbed, and are thus key sites for ore generation.Stable isotopic studies of two deposits within the Duluth Complex have high-lighted the importance of country rock contamination in the generation of Cu—Ni ores. For the Dunka-Road deposit devolatilization of country rocks has resulted in essentially in situ contamination, and the formation of ore that is variable in both its spatial distribution and δ34S values. Partial melting and major element contamination are restricted to areas near the margins of xenoliths. At the Babbitt deposit, contamination via both partial melting and devolatilization has been significant. Sulfur isotopic distribution between igneous and metasedimentary rocks suggests that sulfur must have been derived prior to or during magma ascent. Partial melting of country rocks and oxygen isotopic exchange may have occurred either before or after magma emplacement. Chemical diffusion, as well as fluid dynamic properties of mixing are thought to control the isotopic inhomogeneity that characterizes sulfide ore zones in the Duluth Complex.

Nickel-copper sulfide deposits associated with rocks of komatiitic affinity may be divided into two associations on the basis of host rock composition and ore distribution: (1) stratiform, massive-matrix-disseminated sulfides hosted by cumulate komatiite lava flows (lava conduits), or strata-bound, coarse disseminated sulfides hosted by cumulate komatiite bodies near volcanic vents, and (2) strata-bound, finely disseminated sulfides and more restricted massive sulfides hosted by subvolcanic komatiitic dunites (high-level magma chambers). These deposits represent a continuum in environments of emplacement from distal volcanic through proximal and central volcanic to subvolcanic.Field relationships and geochemical data suggest that the sulfides in these deposits are magmatic in origin. Previous models for their formation involve derivation of sulfides directly from the mantle or from low-level magma chambers, but there are several field, physical, and thermodynamic constraints which suggest that this may not be feasible: (1) the spatial concentration of mineralization within certain pans of otherwise virtually barren host units suggests that the latter were not uniformly saturated in sulfide at the time of emplacement; (2) there are physical problems in transporting dense sulfides in low viscosity komatiite magmas, although dispersed sulfide droplets may be supported during rapid ascent; and (3) high temperature komatiitic melts generated by high-degree partial melting, or sequential melting, of mantle source rocks are unlikely to be sulfide-saturated in the source region or to remain sulfide-saturated during adiabatic ascent. These deposits are, however, commonly associated with specific country rocks, particularly sulfidic sediments, and the distribution of the ores appears to be related to the distribution of these rocks. It is most likely that the sulfide ores exsolved from the komatiitic magmas in situ, in response to assimilation of the country rocks during emplacement. The distribution and texture of the mineralization was probably influenced by (1) the mode of emplacement (volcanic vs subvolcanic) and amount of assimilation; (2) the relative volume of magma (lava conduit vs magma chamber) and its capacity to dissolve sulfur; and (3) the timing of sulfide separation and opportunity for segregation.A fundamental aspect of this model is the coincidence of cumulate komatiitic host units (representing dynamic lava conduits and magma chambers) and siliceous, sulfidic, or ferric iron oxide-rich sediments, the former representing a source of heat for assimilation and of ore metals, and the latter a source of sulfur or of components to induce sulfide separation. Mineralized greenstones appear to have formed in deeper water under conditions of greater extension than unmineralized greenstones; rifting environments represent the most favorable tectonic environment for voluminous komatiite eruption/irruption and for accumulation of sulfidic sediments. Variations in the degree of extension along or within the rift may influence the mode of komatiite emplacement and therefore the type of deposit.

Volcanic peridotite-associated Fe—Ni sulphide deposits in the Archaean Yilgarn Block of Western Australia display a strong volcanological control on the distribution of individual ore shoots. Although considerably modified by tectonism and amphibolite facies metamorphism, there are distinctive stratigraphic relationships within the host ultramafic komatiite sequence that distinguish ore environments from adjacent areas barren of Fe—Ni sulphides.At the well documented Kambalda Dome deposits, contact ores which occur at the base of the lowermost flow of the ultramafic sequence are commonly confined within narrow (100–300 m), elongate embayments or troughs in the underlying tholeiitic footwall metabasalt. Hangingwall ores occur at the base of immediately overlying flows and generally directly overlie the troughs and contact ores.Compared to adjacent barren areas, ore environments are characterized by thicker more-magnesian basal ultramafic flows, fewer interflow metasediments and better textural development and compositional differentiation in overlying thin flow units. The ultramafic sequence overlying ore environments is generally less ordered than that in adjacent non-ore environments where there is a more consistent trend of diminishing magnesium content upward through the ultramafic sequence.The major ore-confining troughs are interpreted as original elongate linear depressions within the footwall metabasalt, and some of the local ore-confining structures probably represent original topographic or volcanological features. Ore deposition in an active rift environment may account for the close spatial relationship of contact and hangingwall ores, and the development of the distinctive stratigraphic features of the ore environment. Analogies are drawn with oceanic rift systems and recent submarine volcanism.

A recent interpretation of regional gravity and magnetic data (Gupta et al. 1984) has indicated that the Sudbury Igneous Complex is underlain at depths of 5–8 km by a 60 × 40 km mass of mafic and ultramafic rock that is not part of the exposed Complex.The marginal rocks of the Complex are thought to have crystallized in situ. The high SiO₂ and K₂O and low CaO contents, and low Na₂O/K₂O ratio of these rocks in comparison with those of continental flood basalts are suggestive that the magma responsible for the Complex experienced extensive contamination by felsic country rocks. The REE profiles and major elements can be modelled if a 1:2 mixture of quartz monzonite and tonalite that form much of the basement at Sudbury, is combined on a 1:1 basis with a fairly primitive flood basalt (MgNo = 0.61). The sublayer is more fractionated than the marginal unit of the main mass, but its major element and REE concentrations also suggest significant assimilation of a similar contaminant. The high Sr initial isotope ratios of both main mass and sublayer are consistent with the contamination hypothesis.Mafic and ultramafic inclusions are restricted to variants of the sublayer that are also mineralized. These inclusions have REE profiles with similar high La/Yb ratios to those of the main mass and sublayer. The Fo content of olivines in the inclusions indicates that they crystallized from liquids spanning the same range of Mg Nos as is spanned by samples of the sublayer. It is proposed that the inclusions have been derived from cumulate layers that formed as the sublayer magmas fractionated.The contamination that gave rise to the SiO₂-rich composition of the Complex is believed to be the cause of the segregation of large amounts of sulfide. It is suggested that the close association between sulfides, inclusions and sublayer magmas is the consequence of the sulfides and ultramafic and mafic cumulates settling together in hidden sills that are present peripheral to and beneath the Complex. These are responsible in part for the gravity and aeromagnetic anomalies. They were injected into the fractures in the rocks beneath the Complex as offshoots from the main magma conduit. As they cooled and fractionated, residual magma rose to the floor of the crater that now holds the Complex to form the presently exposed sublayer. Where magma from a deeper sill cut and disrupted an overlying sill, it picked up sulfides and inclusions, and carried them upwards to form the ore deposits.The magma of the main mass of the Complex, cooling in part within the central conduit, did so more slowly than the sublayer. It thus became contaminated more rapidly, but fractionated less rapidly. It was injected into its present position as a series of pulses at essentially the same time as the sublayer, possibly in response to structural adjustments taking place in the overlying crater.

Some general problems of the formation of copper-nickel ores are discussed on the basis of new data from the Norilsk deposits. These deposits, together with the deposits of greenstone belts and some others, are classified as the deposits connected with ore-bearing volcanic-intrusive complexes of intercontinental rift zones. Massive sulfide ores, sulfide-bearing intrusions, and ultramafic volcanites are shown to have been formed as the result of successive emplacements of magmatic melts formed in the process of deep differentiation of mantle magmas. The factors determining the zonality of distribution of sulfide mineral assemblages in sulfide-bearing intrusions of the bodies of massive sulfides and the formation conditions of platin-bearing horizons of layered intrusions are discussed.In the recent decade, studies of copper-nickel deposits have been undertaken within the International Program of Geological Correlation. A number of basic works aimed at investigating copper-nickel deposits were carried out in the USSR. These studies have contributed significantly to a better understanding of geological and petrological regularities of sulfide ore formation.A concept of the magmatic origin of copper-nickel ores as products of the evolution of ultrabasite-basite sulfide-silicate magmatic systems is emerging. Investigations of ancient copper-nickel ore deposits in greenstone belts of the Archean cratons were especially important in this respect. Presently, the results obtained, as well as the achievements in studies of evolution of structures and endogenous ore formation through the Earth’s history (Kazanskii 1983, Smirnov 1982), allow us to consider the copper-nickel ores as a specific type of magmatic product formed in the course of definite structural transformations of the continental crust.

Ore-bearing formations and copper-nickel deposits are recognized as follows: (1) Duluth-type gabbro-troctolite formation; (2) Norilsk-type gabbro-dolerite formation; (3) Bushveld and Monchegorsk-type gabbro-norite-pyroxenite-peri- dotite formation; (4) Pechenga-type gabbro-pyroxenite-peridotite formation; (5) Kambalda- and Aliarechensk-type pyroxenite-peridotite formation; (6) Mount- keith-type peridotite-dunite; and (7) regenerated Subdury-type diorite-norite formation. Nickel-bearing structures are noted in the greater thicknesses of the Earth’s crust and in downwarped Moho boundaries in weakly eroded provinces. There is a clear relationship between magmatic thicknesses of continental depressions and their ore potential: the thickness of volcanogenic units in ore-bearing structures is over 3 km, whereas that of barren structures is less than 2–3 km. In undislocated areas, the relation between the morphology of intrusive bodies and their ore potential is observed. Ore-bearing magmatic bodies are typically elongated, band-chonolitelike bodies with flat roofs and downwarped bottoms; this is attributed to the excess of density of ore-bearing magmas over that of environment (at the expense of sulfide load) and gravity field effect during intrusion of the bodies that brought about one-way movement of magmatic masses.

Three stages are apparent in the formation of the nickel-copper sulfide deposits, viz. magmatic, regional metamorphic, and late metamorphic. In the magmatic stage, syngenetic ores are simple and constant in the composition formed. In the regional metamorphic stage, epigenetic ores appear that are distinguished by diversities in mineral composition, typical of the specific tectonic zones formed during such metamorphism. Late metamorphic alteration is confined to local tectonic zones and is characterized by the inconstancy of the mineral assemblages. In the process of metamorphism, the chemical composition of the mineralized rocks experiences less alteration that results in a reduction of the geochemical contrast of their separate varieties. All metamorphic alteration events took place within the primary ore bodies and did not result in the formation of new ore shoots. Thus, the Ni—Cu sulfide deposits of the region can be classed as metamorphosed magmatic deposits rather than metamorphic deposits.

Proterozoic mafic and ultramafic intrusive rocks are widespread in the Archaean Kuhmo greenstone belt, including three minor Ni—Cu deposits. Similar intrusions have also been found in the Koli area cutting Jatulian metasediments and the underlying granitoid basement. They are incorporated in the same magmatic association “the gabbro-wehrlite association” as the Ni-bearing intrusions of Pechenga. The cumulate sequences in the layered bodies include olivine, olivine-clinopyroxene, clinopyroxene, clinopyroxene-magnetite, and plagioclase-clinopyroxene-magnetite cumulates. Ti-rich amphibole and mica occur abundantly as postcumulus phases in ultramafic rocks. The chemical compositions of the minerals and rocks differ from those of the Pechenga intrusions, reflecting differences in the parent magmas and their fractionation stages. The parent magmas in eastern Finland and Pechenga are similar to picrites of the Suisaarian and Pechenga types, respectively.

Komatiite magmatism of the Archean greenstone belts of the southeastern part of the Baltic shield is considered here. The conformable bedding and interbedding of bodies of komatiites with pillow basalts and horizons of tuffs, with breccias at their tops, pillows, amygdules, glass and spinifex textures permit the determination of these rocks as peridotite komatiite lavas. Plutonic analogs of these rocks are found in ultramafic effusion feeders. Nickel-copper ore mineralization is orthomagmatic and is associated with komatiitic intrusives. The nickel ore potential of units associated with komatiite magmatism seems to be correlated with the appearance of island-arc basalts: the larger these are, the smaller the ore potential of the structures. And, in this sense, the nearest analogs of the belts in the Baltic shield are the Canadian greenstone belts, not the Western Australian. These may be considered geotectonically as nickeliferous provinces.

Five selected chromium deposits of China are described: Luobusa of Xizang (Tibet), northwestern and northern Inner Mongolia, western Henan, and Panzihua of Sichuan. The first four are podiform deposits and the fifth is stratiform. Six selected nickel deposits of China are described: Jinchuan of Gansu, Dali and Ailaoshan of Yunnan, weathering products near Ailaoshan, and sedimentary nickel deposits of Yangzi craton. These nickel deposits can be classified into four types according to their geologic settings: 1.Rift valley deposits — Jinchuan and Dali2.Obducted ophiolites — Ailaoshan3.Weathering products — near Ailaoshan4.Sedimentary rocks — Lower Cambrian black shales of Yangzi craton

As an introduction to this portion of the Symposium on Copper Deposits, this paper reviews recent progress and findings in research on deposits associated with hypabyssal epizonal plutons. The I-type affinity porphyry copper-molybdenum series is first established as petrogenically distinct from deposits associated with S-type, generally 2-mica granites, the porphyry tin — tin granite — uranium granite suite. Then five specific areas of advance in the 1970s and 1980s are described. The first deals with plate tectonic settings and the global geologic-lithologic distribution of porphyry base metal deposits (PBMDs). Second, the significance of the recognition of changes in the ratio of magmatic to meteoric fluids during alteration-mineralization and deposit emplacement is discussed, along with the concept of “phyllic overprint” and its applications. Techniques for observing, measuring, and describing the propagation of fluids and fracturing in time and space are given. Third, experimental studies, thermodynamic modeling, stable and radiogenic isotope analyses, and fluid inclusion chemical analysis and microthermometric studies and results that have advanced our understanding of the geochemical and thermal nature of PBMD fluids are cited. Fourth, geomathematical modeling studies that describe probable fluid source areas, flow paths, kinetics, and the volume hydrothermally influenced by the emplacement of PBMD systems are considered, and finally the present status of our understanding of PBMD fluids in terms of T, P, f(0₂), f(S₂), salinity, and ion complexing are briefly stated. It is pointed out that the promise of the next decade is enormous if field and laboratory studies continue to loop back to support and extend the whole, and if research continues at its present pace.

The geochemical behaviour of molybdenum and copper during the formation of copper-molybdenum ore deposits is considered. Molybdenum and copper mineralization is closely associated with the hydrothermal-metasomatic associations. The probable values of the physicochemical parameters of copper- and molybdenum-bearing hydrothermal solutions are estimated on the basis of calculations and experimental data. The problem of the types of copper and molybdenum species in ore fluids is considered. Hydroxyl alkali chloride or alkali molybdate complexes are suggested as the molybdenum-bearing species responsible for ore transport. Copper chloride complexes are suggested as copper-bearing transport forms. Cooling of the hydrothermal solutions appears to be one of the main ore deposition factors.

In the course of our study of the porphyry copper deposits of Mexico, the author became aware of the vast extent of the composite batholiths of Sonora and Sinaloa. We observed that the mineralized porphyritic plutons intrude the pene contemporaneous batholith and are associated with dominantly andesitic volcanism. An explanation of this phenomenon is provided by the phenomenon of dome-in-dome structures observed by Ramberg (1981) in centrifuge model experiments where less dense material is overlain by material of greater density. I have applied this concept to the case of a cooling batholith. The interior of a batholith is inherently unstable gravitationally with respect to the more rapidly cooling upper part which is in contact with the country rock. As a consequence, the upper reaches cool faster, begin crystallizing sooner, and eventually become denser than the lower reaches. Thus, the interior of the batholith becomes buoyant and intrudes the upper part. The early batholith forms a broad, gentle dome intruded by later domes. The process is repeated with buoyant upwelling of the interior of the intrusive domes forming cupolas, some of which breach the surface and form cones or stratovolcanos.As a result of the severe temperature regimen and dome-in-dome structures, large-scale hydrothermal fluid transfer occurs dominated by volcanic orifices constituting hydrothermal “pumps” or “artesian vents”. Blind porphyries, those that do not breach the surface, have hydrothermal systems that are subsidiary to the master volcanic artesian vents. Such master hydrothermal systems have isotopically dated lifetimes equal to the isotopically dated long-lived hydrothermal activity of stratovolcanos, i. e., up to at least 2.5 m. y. The fluids exported to the volcanic pumps carry ore components extracted from the batholith and country rock. The ore components are distributed and precipitated in the manifold forms of occurrence observed within porphyry systems.

At least 80 porphyry copper centres, 18 of them major deposits, are known from the central Andes of Chile, Argentina and southern Peru. They are assignable to four longitudinal sub-belts of Meso-Cenozoic age, which become progressively younger from Late Cretaceous in the west, through Paleocene and Late Eocene-Early Oligocene, to Middle-Late Miocene in the east. A fifth, Late Carboni-ferous-Early Permian sub-belt is overprinted by the Middle-Late Miocene sub-belt.The porphyry copper sub-belts are underlain by sialic crust ranging from about 35 to 60 km in present thickness. Outcropping pre-Mesozoic basement rocks range from 2,000-m.y. granulites to Paleozoic magmatic and sedimentary units.Hypogene Cu/Mo ratios of major deposits range from 22 to 88. No systematic variation in Cu/Mo ratios is discernable within or between the three Cenozoic sub-belts. Neither are ratios dependent on the lithology or age of known pre-Mesozoic basement rocks, nor on crustal thickness.The lack of correlation between Cu/Mo ratios and spatial or upper-crustal parameters is consistent with derivation of the principal metals in the porphyry copper deposits from subcrustal levels. The fact that the regionally extensive series of temporally and spatially discrete sub-belts parallels the axis of the Peru-Chile trench, and migrated systematically away from it, strongly supports involvement of fundamental subduction-related processes in the liberation of metals incorporated into central Andean porphyry copper deposits.

Volcano-plutonic belts (VPB) that host porphyry-copper deposits are grouped into basaltic and andesitic types. Basaltic (eugeosynclinal) VPB give rise to island-arc barrier zones (fore-arc). Andesitic VPB originate in an orogenic-activation regime and, depending on the character of the basement, are sub-divided into epicratonic, epimiogeosynclinal, and epieugeosynclinal types. Ore genesis products within the VPB are consistent with vertical and lateral-temporal metallogenic zoning (MZ). In basaltic VPB, copper and gold porphyry-copper deposits are associated with copper massive sulfide ores and are replaced in time by veined polymetallic, and in places, skarn mineralization. MZ of andesitic VPB is controlled by metallogeny of their basement combined with molybdenum-, copper-molybdenum porphyry, and molybdenum-copper deposits (depending on the substratum) as well as with later porphyry Sn, Sn—W, W—Mo, W, Au—Ag ores. The metallogenic style of the VPB is determined by the formation of porphyry deposits. The metallogenic zoning of the VPB is exemplified in some provinces of the Soviet Union.

A generalized geological-structural modeling of porphyry copper deposits reveals the common features of formation of the high-grade ores of the inner parts of stock works. The common internal structure of the ore stock works has been established. The ore stockworks form a series of bodies concentric in plan, whose copper concentration decreases outward from the centre. Studies of the Almalyk area show that the morphology of ore stockworks and high-grade ore parts of chalcopyrite-bornite ores is determined by the form of the stock roof, particularly by the presence of ore-localizing negative structures — depressions, cavities and trenches. The so-called structure of “an egg in a wineglass” is the prototype of high-grade core sections of porphyry copper ores enveloped by the tongues of porphyritic stocks at Almalyk. Low-grade ore envelopes the high-grade ores, smoothing their outline and filling up the irregularities of the stock roof.

Copper-molybdenum mineralization in Mongolia is localized within the limits of regional structures referred to as the superimposed metallogenic belts. The latter is spatially controlled by the late Paleozoic (in Southern Mongolia) and late Paleozoic-early Mesozoic (in Northern Mongolia) volcanic belts, elongate in a sublatitudinal trend. The through-going transverse fault system of the northwest trend has played an important role in forming ore-concentrating structures. Intersection of transverse faults and ones that trend along the volcanic belt account for the development of a block fabric and highly permeable zones that are favourable for the existence of long-lived magmatic centers that host the ore fields.

The following conclusions can be drawn concerning the genesis of the Recsk deposit: 1.The mineralization belongs to the Paleogene volcanic arc along the Balaton-Darno line.2.The main phases of mineralization, culminating with porphyry copper formation, are products of hydrothermal events related to a diorite porphyry intrusion (a₃ stage).3.The two younger (post-intrusion) volcanic cycles have resulted in late-stage near-surface mineralization, which is considered to be a product of remobilization. In comparison with other porphyry copper mineralization it may be suggested that the Recsk deposit has an affinity with the island-arc-type magmatism. It shows similarities with the diorite model in the zoning of the intrusive rocks and the ore distribution. Morphogenetically it may be termed a “conformable” deposit. Its classification was simplified by the completeness of the ore depositional sequence, although the sequence of superimposed ore-forming stages created difficulties for interpretation.

Ore deposition concludes a complex cycle of transport and evolution of materials throughout the crust (20–30 km thick) where magmatic and hydrothermal associations, derivatives of a single ore-magmatic system, are being formed. Ore formation takes place in or near porphyry stocks considered as cupolas of intermediate magmatic chambers, the crystallization of which markedly influenced the formation of the flow of ascending fluid as well as a total temperature rise. The zone of magmatic cupolas (stocks) is characterized by more intensive ascending fluid flow. Here, favorable conditions for magmatic- hydrothermal systems exist. Conditions of mineralization in the hypabyssal environment become more complex because of the anatectic chamber, the crystallization of which causes an additional fluid flow into the upper levels of the crust. The development of the ore-magmatic system results from the interaction of subcrustal mafic magma and fluids separating from it with a magmatic melt formed in the crust. Fluids of two types existed in forming copper-molybdenum deposits. The magmatic system includes concrete intrusive bodies of an ore-bearing magmatic complex and the rock volumes adjacent to them. The meteoric-hydrothermal fluid system does not evolve in close juxtaposition with these intrusives.

The Spanish-Portuguese Pyrite Belt covers a large area in the SW part of the Iberian Peninsula. Known reserves of massive pyrite and cupreous stockwork ore exceed 1000 million tons.The stratiform sulphide deposits and accompanying manganese mineralization are of synsedimentatry-exhalative origin and occur in a Lower Carboniferous, geosynclinal, volcanic-sedimentary rock sequence, strongly folded during the Hercynian Orogeny. Epigenetic stockwork ores are in close relationship with volcanism and often represent the feeder channels of the massive sulphide sedi-ments.Most important ore types mined are massive “crude” pyrites, lead-zinc-rich “complex” pyrites, high-copper “banded” ores, copper-rich stockwork ores, disseminated “porphyry”-type copper ores and gold-silver-rich gossans. The main active mines are described and beneficiation of these ores is discussed.

This paper analyzes metallogenic specialization of two pairs of pyrite-bearing structural-formational zones2 belonging to the Caucasian segment of the Mediterranean fold belt. These zones evolved during the Alpine tectono-magmatic cycle along the northern and southern framing of the Transcaucasian microcontinent. In the northern pair (the Great Caucasus meganticlinorium) the pyrite-bearing zones are in the central trough and the south continental rise, and in the southern pair (the Lesser Caucasus meganticlinorium), they are in the rift ophiolitic zone and the island arc. A clustering concentration pattern of base- metal mineralization with centrifugal and centripetal types of localization of pyrite, porphyry and vein deposits has been revealed.

The hidden mineralogical and geochemical zoning (HMGZ) of the repeated and nonrepeated structural types is characterized by examples of different massive sulfide deposits of Karelia, South Urals, Rudni Altai, and Japan. This zoning is detected in different scale orders by means of microanalysis through the composition variations of the ore-forming sulfides: pyrite, sphalerite, and tennantite-tetrahedrite. Is is shown that in the case of primary origin of such zoning its nonrepeated type corresponds to volcanic-sedimentary ore deposition and repeated type - to a hydrothermal replacement one. It is established that the variations of Co/Ni values or Co-content in pyrite, Fe-content in sphalerite, As-, Sb-, Ag-content in tennantite-tetrahedrite in cross-sections of the individual ore bodies (ore intervals, rhythms) are mainly due to alteration of temperature and sulfur activity during ore formation.

Vertical and lateral zoning of massive sulphide deposits is well known. Vertical zoning is characteristic of volcanic-hosted deposits (e. g. Kuroko), whereas lateral zoning occurs in sediment-volcanic-hosted ore (e. g. Zhairem). A dynamic model of such zoning would belong to the “barrier reaction” type. An oxide-acidic model is herein proposed for the volcanic-hosted and a reduced-carbon model for the sediment-volcanic-hosted deposits. The first model relates to the boundary of the metalliferous solutions/oxidized water system. Oxidized sulphur components in this system range from S0₂ to S2−. The acidity and ratio of S2−/SO₄2− are increased and decreased, respectively, from the base to the upper part of the ore section. The result of these variations is the following sequence (from bottom to top): sulphide-silicate metasomatites, pyrite-, copper- and lead- zinc-pyrite massive ores. The form and size of these ore types is caused by the dynamics of the hydrothermal flow and the size of the recycling zone. According to the reduced-carbon model, the ore is deposited from the hydrothermal brine into depressions on the seafloor. Deposition is controlled by the brine/seawater contact, where sulphate-reduction takes place. The laterally concentric emplacement of lead, zinc and pyrite ores is caused by depletion of the sulphidic ion and concentration of the metallic ions in the brine pool.

Primary base metal massive sulphide deposits are formed as a rule in seafloor depressions. Ore formation is preceded by stratification of seawaters into oxiding and reducing zones. Hydrothermal sedimentary pyritic bodies are formed in two stages. During sedimentogenesis, monosulphide iron and non-ferrous thin sediments are accumulated under thermodynamic disequilibrium conditions. During diagenesis, sea-floor sulphide sediments are crystallized as a result of their interaction with pore solutions. The latter, according the thermodynamic data, are characterized by the buffer ratio of sulphur in oxidized and reduced forms. The process of diagenesis results in standard base metal zonation. If pyrite-bearing fluids are characterized by increased total activity of sulphur, then such a zonation is complicated by an additional zonal distribution of sulphides and sulphates. The disappearance of anhydrite at the barite-polymetallic level is due to the spontaneous evolution of the external physical and chemical parameters against a background of temperature decrease and displacement of the invariant barite-calcite-anhydrite equilibrium towards to barite crystallization field.

The barite bed at Fukazawa mine overlies a massive black ore zone and underlies a ferruginous chert bed (tetsusekiei). It is characterized by simple mineralogy which consists predominantly of barite with small but variable amounts of pyrite, sphalerite, chalcopyrite, galena, hematite, quartz and traces of intimately intergrown chlorite-sericite. Chemical and textural evidence indicates that barite formed by the mixing of a circulating barium-rich hydrothermal solution with cold seawater within an unconsolidated pyritic tuff. Growth of barite displaced the very fine silicate matrix through a process of fluidization of the tuffaceous bed during hydrothermal discharge. Variations in the intensity of the hydrothermal activity resulted in vertical fluctuations of the redox boundary providing for replenishment of the barite environment with cold seawater which passed on to the barite both its sulfur and strontium isotopic characteristics. The barite bed was affected by later hydrothermal solutions, the activity of which continued even after the deposition of hanging wall rocks. As a consequence, equilibrium thermodynamics cannot be applied to describe the chemical behaviour of the bulk dynamic system.

Disseminated copper and copper-iron sulfide mineralization at the White Pine (Michigan), Redstone (N.W. Territories, Canada) and Kamoto (Shaban Province, Zaire) deposits are interpreted to have been emplaced during early diagenesis by an influx of dissolved copper into initially pyritic basal units of grey-bed host rocks. This concept is supported by the position and configuration of the mineralized zones, by numerous textural features, by the zoning of Cu- and Fe- bearing sulfides as well as affiliated metals (e. g. Pb, Zn, Co and Mo), and by comparisons with modern analogs of strata hosting stratiform copper deposits. Most evidence supports an early diagenetic introduction of copper from underlying coarse-grained red beds. Plausible sources of copper include the red beds themselves, or pene-exhalative solutions which “exhale” into the red beds. Preliminary quantitative data now available suggest that the red beds may have provided sufficient copper to mineralize basal units of the overlying grey beds; the tectonic setting and timing of mineralization also encourage further research into the pene-exhalative model.

The stratiform copper-cobalt mineralization in the Shaban Mines Group took place in intertidal sediments enclosing the stromatolitic masses of the R.2.1.3 unit and around similar masses corresponding to the R.2.3.1 unit.The cristallization of primary sulphides displays a vertical zoning with pyrite at the base and at the top of the ore bodies. They form micro- and macrocycles suggesting a sequence of copper and cobalt mineralization. This mineralization results from a diagenetic process involving a mixing of stagnant interstitial water with brines which were enriched in metals and which migrated through still porous sediments. Secondary reactions with the brines enriched previously formed sulfides with additional copper and/or cobalt.

Noneconomic red-bed copper occurrences in the Devonian Catskill Formation are localized by concentrations of reducing plant fragments, commonly in the basal parts of fining-upward fluvial (or tidal?) cycles. The occurrences are within and near thick zones of red mudstone to fine sandstone interpreted to have been deposited in relatively inactive parts of an extensive alluvial plain in an arid environment. Regionally, the occurrences are most abundant adjacent to areas of major sediment input, and in more detail are controlled in part by sandstone beds which were more mature and probably more permeable than the rest of the formation. The copper minerals were emplaced after earliest diagenesis, but before induration and formation of quartz overgrowths. Thin zones of transgressive marine sandstone are present near most occurrences. Copper has been redistributed within the Catskill, being greatly depleted from nearly all red (oxidized) sediments, but showing highly variable values in green and gray (reduced) sediments. Mobilization of copper from the red beds into chloride- bearing pore fluids of marine or evaporative origin is proposed, followed by flow of these fluids through the more permeable sandstones until organic reductants were encountered which precipitated the copper by bacterial sulfate reduction. The flow was driven by compaction, sea-level changes, and gravity flow down the alluvial plain. Red beds near the Coates Lake stratiform copper deposit in the Redstone area show similar depletion of copper.

Six stratabound Kennecott-type copper deposits are being studied to evaluate the characteristics of the ore-host rock system. Three (Mountain Grill, Radovan, and Clear-Porcupine) are in the Middle to Upper Triassic Nikolai Greenstone — a thick sequence of subaerial amygdaloidal tholeiite flows — and the other three (Binocular, Nelson, and Peavine) are in the Upper Triassic Chitistone Limestone, a platformal limestone and dolomite unit.X-ray diffraction, petrographic and chemical studies have led to the identification of ten ore minerals in the deposits, the most abundant being digenite, chalcocite, djurleite, covellite, bornite, and chalcopyrite. Minor arsenic and antimony sulfide phases are also present. Mineral deposits in greenstones have both Cu and Cu - Fe sulfides in contrast to the essentially Cu-sulfides in limestones.The mineralization is proposed to have formed in two stages. Hydration-dehydration reactions associated with alteration-metamorphism of the Nikolai Greenstone liberated copper from the metal oxides and the mafic minerals. Copper was carried by the circulating fluids along the existing fracture-fluid pathway system, reacting and precipitating ore minerals in them. The weak and widely distributed mineralization in the belt is probably of this type. Greenstone alteration was probably coincidental with Cretaceous accretionary orogeny as shown by K- Ar systematics (Silberman et al. 1981).Cenozoic deformation induced a steep fracture system that enhanced the porosity and permeability of the rocks, thus focusing the meteoric water circulatory system for effective and efficient solution and transport of metals. Activity in such a system at this stage was probably driven by a thermal charge from the Tertiary intrusives. Lack of extensive alteration of the Chitistone Limestone and of recrystallization at the ore vein-limestone contacts suggests that the ore solutions were at relatively low temperatures. The mineral associations and textures suggest that the upper temperature that prevailed in the Triassic ore-host rock system was about 200 °C.

The chemical compositions of fine-grained sedimentary rocks provide important genetic indications when their mineralogical significance is brought out. The chemical approach is essential when the primary features have been obliterated by metamorphic crystallization. Recent progress in the geochemistry of shales and marls from evaporite-bearing series is of special interest with regard to sediment-hosted copper deposits.Two major chemical characteristics are obvious in the environment of the Ore-Shale deposits in the Zambian Copperbelt based on comparison of 378 analyses on systematically chosen samples from drill holes and cross-sections in Konkola, Chingola, Chambishi, Mindola, Rokana, and Luanshya (metamorphism from greenschists to lower amphibolite facies) with shales and marls from common platform series. Firstly, the relatively high Mg (and Li) contents are characteristic of magnesian clay minerals, in the early members of evaporitic sequences. This is an ubiquitous feature whereas anhydrite is only of local occurrence. Secondly, primary (premetamorphic) fine-grained rocks with very high K- feldspar and comparatively low quartz contents (around 63% feldspar, 10% quartz and 27% chlorite-rich clays) are inferred from extremely high K₂O concentrations (often ≥10%) and K/Al ratios in the Ore-Shale Formation. These compositions cannot be obtained by sedimentary processes only and a large part of the feldspar is probably of diagenetic/hydrothermal origin.In Shaba (Kamoto, Kambove) the Cu and Co concentrations are carbonate- hosted. However, very uncommon chemical compositions are exhibited by the Mg-chlorite-quartz-dolomite rocks of the underlying RAT formation (32 analyses): high Mg, Li and low alkali contents. They could partly derive from felsic-volcanic glass altered by reaction with Ca- and Mg-rich and alkali-poor brines. Such brines have been observed in fluid inclusions related to U-mineralization which occurs at the top of the formation.In contrast, the German Kupferschiefer (Mansfeld district, 22 analyses) does not show major element compositions different from those of common black shales.

The palaeogeographic situation of the Fore-Sudetic Monocline during the first Zechstein evaporative subcycle, evolution of the metalliferous sedimentation and subsequent subaerial geological processes are illustrated on a redox map, geochemical profiles and diagram. The sequence of the sedimentation of the seaward and lagoonward slopes of the lagoonal barrier explains the differences between copper- and lead-bearing shale sedimentation environments. Subaerial abrasion, redeposition, oxidation, cementation and lagoonal brine infiltration contributed to the redistribution of metals in the just-formed sediments before Werra main dolomite sedimentation closed the first evaporative subcycle.

The concept introduced here suggests a common provenance of copper origin for all cupriferous sandstones and shale-type deposits, the source of copper being terrigenous red-bed formations deposited under arid conditions. Copper was leached from these rock deposits by subsurface waters. Copper precipitation occurred at hydrogen sulphide barriers, among which two types are recognized: syngenetic (in unconsolidated sediments) and epigenetic (in lithified sediments). The latter are subdivided, according to the origin of their organic matter, into autochthonous and allochthonous groups. The decisive factor controlling the formation of sediment-hosted copper deposits with large reservers is the specific nature of the paleohydrogeological and geochemical environment.Copper-sandstone and copper-shale deposits represent a highly specific group of deposits, distinguished by the following characteristic features: (1) invariable spatial association with red beds formed in an arid environment; (2) ore localization in grey sedimentary rocks in close proximity to the red beds; (3) consistent mineral composition and associations of major metallic minerals; (4) a zonal distribution pattern of the sulphides in the ore bodies.Three hypotheses have been discussed by researchers for the origin of the metallic substances in this group of deposits: hydrothermal (endogenetic solutions), sedimentary (provenance area), and exogenetic-epigenetic (subsurface pore waters of arid red-bed formations). The validity of the above-cited hypotheses can readily be weighed: if it is true that they should provide a lucid understanding for the known spatial association of copper mineralization with arid red beds. This relationship, repeatedly verified by field observations, can be regarded as a well-founded empirical law; nevertheless, it is commonly ignored by the proponents of the hydrothermal hypothesis. A similarly adequate solution of the source problem has been offered by the supporters of the sedimentary hypothesis. According to the latter, advocated by Strakhov (1963), copper was leached from ore deposits of humid provenance by surface waters, and redeposited in arid regions in the form of carbonates that subsequently underwent conversion to sulphides during early diagenesis. However, the original copper carbonates have never been encountered. Consequently, it must be assumed that these carbonates were invariably precipitated only in those areas where the oxidizing environment in the sediments underwent a subsequent change to a reducing, hydrogen sulphide environment.The general spatial association of copper mineralization with arid red-bed formations is feasibly explained by the epigenetic hypothesis, but from this viewpoint the characteristics of certain deposits, undoubtedly of sedimentary origin (for example, Mansfeld), has in past years remained incompatible. According to the epigenetic hypothesis, copper was leached from red beds by subsurface waters, and therefore its accumulation in marine sediments was regarded as inconsistent with this concept. In fact, the contribution of copper from bottom sediments to sea basin waters is quite natural, considering that influx to the seas is derived not only from the run-off of surface waters, but also from inflow of subsurface waters. If the waters of red-bed formations drained into the paleosea, then these waters could have been responsible for the copper supply. Hence, the most warranted hypothesis is that copper and associated metals were leached by subsurface waters from red-bed formations. In this respect the deposits under study are a group of closely related deposits, having in common the origin of their metal content.Sulphide mineralization is usually restricted to grey sediments, occurring immediately adjacent to the red beds. This association indicates that the concentration of copper occurs at hydrogen sulphide barriers that are formed at the interface between sediments of markedly different characteristics. The distinctions between deposits are largely due to the conditions under which the hydrogen sulphide barriers are formed. According to the time of formation of the host rocks relative to mineralization, two types of hydrogen sulphide barriers can be distinguished: syngenetic and epigenetic types. The first occur in unconsolidated sediments, the second in lithified rock deposits.

The territory of the Soviet Union is characterized by orogenic, platform and geosynclinal, copper-bearing zones. Major epochs of sedimentary copper accumulation are: Early and Late Proterozoic and Late Paleozoic, favouring generation of orogenic copper sandstone, and Middle Mesozoic, favouring the emplacement of copper — pyrrhotite mineralization in early geosynclinal black shale trough zones.Different ways of evaluating areas with good potential are shown, based on the cyclic recurrence and facies features of copper-bearing sediments, as well as structure of productive strata in deposits.The cyclic pattern of copper-bearing molasse sediments determines the morphology of productive strata, their simple or multicyclic structure. Flyschoid sediments contain copper sandstone with a simple structure of productive strata, having relatively small size.Ore-bearing deposits of arid red beds are divisible into the following zones: (1) copper and polymetallic mineralization in red and variegated sediments of greywacke composition and (2) copper mineralization in variegated and red sediments of arkose composition and displaying thick cycles.

Remobilization of the geochemical background of the ore- and rock-forming elements of red-colored copper-bearing sediments in the Dzhezkazgan ore region has been studied. Potentialities of these deposits as specialized ore-forming systems are shown along with the paragenesis of copper and oil formation, with the biofactor actively participating. The systems elements are clearly distinguished in the geochemical and geophysical fields. The metallogenic classification of the copper-bearing, red-colored formations and the stratiform copper ores of the copper sandstones and slates type connected with them has been worked out. It served as the basis for the formation-metallogenic analysis of the ore content of the red-colored formations and stratolevels of various age (from Upper Proterozoic to Neogene) in Kazakhstan. Areas of occurrence of the commerically perspective formations of the Dzhezkazgan type have been distinguished.

The Siberian platform is host to a variety of mineral deposits, including stratiform copper deposits in sandstones and shales. Six major copper provinces are recognized (Prieniseyskaya, Prisajanskaya, Pribaikalskaya, Prialdanskaya, Priverkhojanskaya, Prianabarskaya), and within these at least 15 major zones of deposits and occurrences, including the Udokan district. The cupriferous sediments occur in Proterozoic and Paleozoic detrital sediments ranging from sandstone to shale, usually either varicoloured or black. Some of the sediments contain carbonate (cement) and some contain volcanic material. The cupriferous sediments are localized around the border of the platform in basins filled with sediment shed from adjacent uplifts. More central parts of the platform contain lead-zinc, barite, fluorite, gypsum-anhydrite, and other evaporite minerals, whereas gold occurs in conglomeratic zones closer to the uplifts. The size and shape of ore zones depend closely on sedimentary facies. On a basin scale, the cupriferous sandstones and shales transgress into younger sediments toward the center of the basin, and are mineralogically zones from underlying pyrite and chalcopyrite in-to overlying bornite-chalcocite zones. Similar circumferential and beltlike zones of cupriferous sediments are recognized around and adjacent to other platforms on all continents. The deposits were formed during sedimentation and diagenesis, but have since been subjected to various combinations of epigenesis, metamorphism and weathering. The sources of copper are considered to be in the up-lifted blocks that supplied the sediment, and in volcanic effusions.The Siberian Platform and its folded border zones is one of the most imporStant metallogenic regions in the world. It is formed almost entirely of sedimentary formations ranging in age from Archean to Cenozoic and including various mineral deposits (Bogdanov et al. 1973, Narkelyun et al. 1977). Cupriferous sandstones and shales are confined to Proterozoic and Paleozoic formations of the platform where the Prieniseyskaya, Prisajanskaya, Pribaikalskaya and Prialdanskaya copper provinces have been established (Fig. 1).

This paper discusses the general regularities of the distribution of the copper mineralization associated with the Vendian red-bed formation. Lean stratified mineralization is restricted to the zones transitional from the red-beds to the underlying and overlying grey-colored rock deposits. Rich ore deposits are spatially associated with epigenetic carbonaceous matter in the highly-permeable coarse-clastic red-beds near the paleo-uplifts.The epigenetic host rock alterations associated with ore deposition, and the copper mineral zonation are discussed. A genetic classification of the copper mineralization in the area is suggested.

The huge sediment-hosted copper deposits at Olympic Dam and Mount Isa are of unusual types. They formed epigenetically from hydrothermal fluids, as did several other important Australian copper deposits in sedimentary strata. Ore within a palaeoweathering zone at the top of a red-bed unit at Mount Gunson appears to have formed at relatively low temperatures over a long period and to have incorporated biogenic sulfur. Bedded-disseminated mineralization, which is wide-spread in South Australia, formed by reaction of cupriferous fluids with biogenic H₂S and early diagenetic iron sulfides. To date, stratiform copper mineralization has not been of major economic significance in Australia.

The zoning typical of many sediment-hosted copper-iron sulfide deposits cannot be well accounted for by equilibrium approaches, which lead to inconsistencies and which are inherently ill-suited to describe a spatial, nonequilibrium process such as zoning. Much better is a kinetic approach that consists of differential equations representing dissolution, nucleation, growth, flow, and diffusion, all of which are clearly involved in ore genesis. In this kinetic model, time and spatial coordinates appear explicitly, and the equations automatically incorporate feedbacks among mechanisms. Numerical solutions of the equations for many combinations of reasonable values of the parameters involved (such as velocity and composition of the mineralizing water, equilibrium and reaction-rate constants, initial amount of pyrite in the rock, diffusion and nucleation constants, and others) can yield mineral zoning of several types, including the typical chalcocite-bornite-chalcopyrite-pyrite found at the White Pine deposit.

In two areas of the Werra-Fulda trough (Hessia, West Germany) exploration of Kupferschiefer-type copper-silver deposits was carried out by St. Joe Explora-tions GmbH Western Europe.Anomalous high copper-silver contents were detected in the Spessart-Rhön area as well as in the Richelsdorf area. Especially in the Richelsdorf area all features connected with the occurrence of economic mineralization are similar to the deposits in Poland.The relationship between grade of mineralization, spatial distribution of metals and minerals, paleogeography and the occurrence of “Rote Fäule” in two St. Joe drill holes and two holes drilled by the BGR (Bundesanstalt für Geowissenschaften und Rohstoffe, Hannover) is discussed.