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1.
Eight Zn–Pb–Cu massive sulphide deposits that appear to have formed on the sea floor (seven in Spain, one in Tasmania) are believed to have been precipitated in brine pools, based on the salinities and temperatures of fluid inclusions in underlying stockworks. Comparing the geological features of these deposits with those of the Zn–Pb–Cu massive sulphide ores of the Hokuroku Basin, Japan, which have formed as mounds from buoyant fluids of low salinity, shows that brine pool deposits have: (1) potentially very large size and tonnage, and high aspect ratio, (2) higher Zn/Cu and Fe/Cu values, (3) no evidence of chimneys, (4) relatively abundant framboidal pyrite and primary mineral banding, (5) reduced mineral assemblages (pyrite-arsenopyrite/pyrrhotite), and minor or rare barite in the massive sulphide, (6) associated stratiform and/or vein carbonates, (7) relatively unimportant zone refining, (8) lack of vertical variation in sphalerite and sulphur isotopic compositions, and (9) evidence of local bacterial sulphate reduction. Application of these criteria to the Rosebery deposit in Tasmania, for which there are no fluid inclusion data, leads to the conclusion that the southern section was deposited as separate lenses in a brine-filled basin or basins. Other potential candidates include Brunswick no. 12 and Heath Steele (Canada), Woodlawn and Captains Flat (New South Wales), Hercules and Que River (Tasmania), and Tharsis and the orebodies at Aljustrel (Spain and Portugal). Recently published fluid inclusion data for Gacun (China) and Mount Chalmers (Queensland) suggest that not all ores deposited from highly saline fluids have reduced mineral assemblages.  相似文献   

2.
Mike Solomon   《Ore Geology Reviews》2008,33(3-4):352-360
Current models of massive sulphide ore genesis in the Bathurst mining camp, New Brunswick, involve settling of sulphide particles from a stagnating, low-salinity hydrothermal plume spreading laterally in an anoxic ocean layer with minimal sulphate content. There is fragmentary evidence of ocean anoxia in the form of local fine lamination in the shales that host some of the deposits but the total organic carbon, S, Fe, U/Th, Ni/Co, V/Ni and V/Cr relationships indicate deposition under oxic or dysoxic conditions. Vanadium and Mn values range from oxic to anoxic and sulphate-reducing to non-sulphate reducing but Mn may be anomalously low due to derivation by erosion of acidic volcanic rocks. The somewhat equivocal physical and chemical data, combined with the likely disturbing effects of penecontemporaneous volcanism, considerably weaken the case for an anoxic bottom layer in a static ocean. The presence of barite with ambient seawater 34S values in Brunswick no. 12 ore, and the abundance of sulphate in modern euxinic basin waters, make a sulphate-free layer unlikely, even if anoxic. Sulphate-bearing, low-salinity fluids mixing with seawater would lead to growth of barite-bearing chimneys and baritic rubble mounds, which are not observed. A model involving brine-pool deposition better explains the major features of the Bathurst ores.  相似文献   

3.
The metaturbidites of the Palaeoproterozoic Jormua–Outokumpu thrust belt in eastern Finland enclose m- to km-scale ultramafic massifs that are distributed over an area of more than 5000 km2. These bodies, which almost entirely consist of highly depleted mantle peridotites (now metaserpentinites and metaperidotites), are intimately associated with massive to semimassive, polymetallic Cu–Co–Zn–Ni–Ag–Au sulphide deposits that sustained mining in the region between 1913 and 1988. Currently, one deposit (Kylylahti) is proceeding into a definitive feasibility study emphasising the renewed economic interest for Outokumpu-type deposits.The origin of these Outokumpu-type Cu–Co–Zn–Ni–Ag–Au deposits is now re-interpreted to be polygenetic. First, their formation requires deposition of a Cu-rich proto-ore within peridotitic sea floor at  1950 Ma. Close modern analogues to the proto-ore setting include, for example, the Logatchev and Rainbow fields at the Mid-Atlantic Ridge, where venting of high-T–low-pH hydrothermal fluid resulted in accumulations of Cu–Zn–Co–Ag–Au sulphides on serpentinised ultramafic seafloor. Second, the Ni-rich composition of Outokumpu sulphide ores calls for a separate source for nickel: Some 40 Ma after the deposition of the Cu-rich proto-ore – concomitant with the obduction of the ultramafic massifs – disseminated Ni sulphides formed through chemical interaction between obducting peridotite massifs and adjacent black schists. This process was related to listwaenite–birbirite type carbonate–silica alteration at margins of the ultramafic massifs. Due to this alteration, silicate nickel was released from the primary Fe–Mg silicates and redeposited as Ni sulphides in the alteration fringes of the massifs.We propose that syntectonic mixing of these two “end-member” sulphides, i.e., the primary Cu-rich proto-ore and the secondary Ni-sulphide disseminations, resulted in the uncommon metal combination of the Outokumpu-type sulphides. Late tectonic solid-state re-mobilisation, related to the duplexing of the ore by isoclinal folding, upgraded the sulphides into economic deposits.  相似文献   

4.
Draa Sfar is a Visean, stratabound, volcanogenic massive sulphide ore deposit hosted by a Hercynian carbonaceous, black shale-rich succession of the Jebilet terrane, Morocco. The ore deposit contains 10 Mt grading 5.3 wt.% Zn, 2 wt.% Pb, and 0.3 wt.% Cu within two main massive sulphides orebodies, Tazakourt (Zn-rich) and Sidi M'Barek (Zn–Cu rich). Pyrrhotite is by far the dominant sulphide (70 to 95% of total sulphides), sphalerite is fairly abundant, chalcopyrite and galena are accessory, pyrite, arsenopyrite and bismuth minerals are rare. Pyrrhotite is monoclinic and mineralogical criteria indicate that it is of primary origin and not formed during metamorphism. Its composition is very homogeneous, close to Fe7S8, and its absolute magnetic susceptibility is 2.10− 3 SI/g. Ar–Ar dating of hydrothermal sericites from a coherent rhyolite flow or dome within the immediate deposit footwall indicates an age of 331.7 ± 7.9 Ma for the Draa Sfar deposit and rhyolite volcanism.The Draa Sfar deposit has undergone a low-grade regional metamorphic event that caused pervasive recrystallization, followed by a ductile–brittle deformation event that has locally imparted a mylonitic texture to the sulphides and, in part, is responsible for the elongated and sheet-like morphology of the sulphide orebodies. Lead isotope data fall into two compositional end-members. The least radiogenic end-member, (206Pb/204Pb = 18.28), is characteristic of the Tazakourt orebody, whereas the more radiogenic end-member (206Pb/204Pb  18.80) is associated with the Sidi M'Barek orebody, giving a mixing trend between the two end-members. Lead isotope compositions at Draa Sfar testify to a significant continental crust source for the base metals, but are different than those of the Hajar and South Iberian Pyrite Belt VMS deposits.The abundance of pyrrhotite versus pyrite in the orebodies is attributed to low fO2 conditions and neither a high temperature nor a low aH2S (below 10− 3) is required. The highly anoxic conditions required to stabilize pyrrhotite over pyrite are consistent with formation of the deposit within a restricted, sediment-starved, anoxic basin characterized by the deposition of carbonaceous, pelagic sediments along the flank of a rhyolitic flow-dome complex that was buried by pelitic sediments. Deposition of sulphides likely occurred at and below the seafloor within anoxic and carbonaceous muds.Draa Sfar and other Moroccan volcanogenic massive sulphide deposits occur in an epicontinental volcanic domain within the outer zone of the Hercynian belt and formed within a sedimentary environment that has a high pelagic component. In spite of the diachronous emplacement between the IPB deposits (late Devonian to Visean) and Moroccan deposits (Dinantian), all were formed around 340 ± 10 Ma following a major phase of the Devonian compression.  相似文献   

5.
The mineralogy and structure of the supergene profile in recently-exploited volcaniс hosted massive sulphide (VHMS) deposits of Cyprus, Uralian and Kuroko type in the South Urals, Russia, have been studied. Specific subzones enriched in secondary sulphides and associated minerals have been distinguished in residual pyrite and quartz–pyrite sands at the Gayskoye, Zapadno-Ozernoye, Dzhusinskoye and Alexandrinskoye deposits. Besides minerals which are common to the cementation subzones (covellite, chalcocite and acanthite), non-stoichiometric colloform and framboidal pyrite, pyrite–dzharkenite, pyrrhotite-like and jordanite-like minerals, metacinnabar, sphalerite, selenium-enriched tetrahedrite and unidentified As-, Sb sulphosalts of Pb or Hg and Ag, sulphur-bearing clausthalite, naumannite and tiemannite were also found. Secondary sulphide minerals in VHMS deposits of the South Urals region are characterized by light sulphur isotope compositions (− 8.1 to − 17.2‰). Superposition of the advanced oxidation of colloform pyrite, an enrichment in impurities (sphalerite, galena, and tennantite) from the primary ores, stagnant water conditions, an elevation of the water table during oxidation, and bacterial activity led to supergene concentrations of the base metals as sulphide, selenides or sulphosalts.  相似文献   

6.
The Neoproterozoic central African Copperbelt is one of the greatest sediment-hosted stratiform Cu–Co provinces in the world, totalling 140 Mt copper and 6 Mt cobalt and including several world-class deposits (10 Mt copper). The origin of Cu–Co mineralisation in this province remains speculative, with the debate centred around syngenetic–diagenetic and hydrothermal-diagenetic hypotheses.The regional distribution of metals indicates that most of the cobalt-rich copper deposits are hosted in dolomites and dolomitic shales forming allochthonous units exposed in Congo and known as Congolese facies of the Katangan sedimentary succession (average Co:Cu = 1:13). The highest Co:Cu ratio (up to 3:1) occurs in ore deposits located along the southern structural block of the Lufilian Arc. The predominantly siliciclastic Zambian facies, exposed in Zambia and in SE Congo, forms para-autochthonous sedimentary units hosting ore deposits characterized by lower a Co:Cu ratio (average 1:57). Transitional lithofacies in Zambia (e.g. Baluba, Mindola) and in Congo (e.g. Lubembe) indicate a gradual transition in the Katangan basin during the deposition of laterally correlative clastic and carbonate sedimentary rocks exposed in Zambia and in Congo, and are marked by Co:Cu ratios in the range 1:15.The main Cu–Co orebodies occur at the base of the Mines/Musoshi Subgroup, which is characterized by evaporitic intertidal–supratidal sedimentary rocks. All additional lenticular orebodies known in the upper part of the Mines/Musoshi Subgroup are hosted in similar sedimentary rocks, suggesting highly favourable conditions for the ore genesis in particular sedimentary environments. Pre-lithification sedimentary structures affecting disseminated sulphides indicate that metals were deposited before compaction and consolidation of the host sediment.The ore parageneses indicate several generations of sulphides marking syngenetic, early diagenetic and late diagenetic processes. Sulphur isotopic data on sulphides suggest the derivation of sulphur essentially from the bacterial reduction of seawater sulphates. The mineralizing brines were generated from sea water in sabkhas or hypersaline lagoons during the deposition of the host rocks. Changes of Eh–pH and salinity probably were critical for concentrating copper–cobalt and nickel mineralisation. Compressional tectonic and related metamorphic processes and supergene enrichment have played variable roles in the remobilisation and upgrading of the primary mineralisation.There is no evidence to support models assuming that metals originated from: (1) Katangan igneous rocks and related hydrothermal processes or; (2) leaching of red beds underlying the orebodies. The metal sources are pre-Katangan continental rocks, especially the Palaeoproterozoic low-grade porphyry copper deposits known in the Bangweulu block and subsidiary Cu–Co–Ni deposits/occurrences in the Archaean rocks of the Zimbabwe craton. These two sources contain low grade ore deposits portraying the peculiar metal association (Cu, Co, Ni, U, Cr, Au, Ag, PGE) recorded in the Katangan sediment-hosted ore deposits. Metals were transported into the basin dissolved in water.The stratiform deposits of Congo and Zambia display features indicating that syngenetic and early diagenetic processes controlled the formation of the Neoproterozoic Copperbelt of central Africa.  相似文献   

7.
The Huize Zn–Pb–(Ag) district, in the Sichuan–Yunnan–Guizhou Zn–Pb–(Ag) metallogenic region, contains significant high-grade, Zn–Pb–(Ag) deposits. The total metal reserve of Zn and Pb exceeds 5 Mt. The district has the following geological characteristics: (1) high ore grade (Zn + Pb ≥ 25 wt.%); (2) enrichment in Ag and a range of other trace elements (Ge, In, Ga, Cd, and Tl), with galena, sphalerite, and pyrite being the major carriers of Ag, Ge, Cd and Tl; (3) ore distribution controlled by both structural and lithological features; (4) simple and limited wall-rock alteration; (5) mineral zonation within the orebodies; and (6) the presence of evaporite layers in the ore-hosting wall rocks of the Early Carboniferous Baizuo Formation and the underlying basement.Fluid-inclusion and isotope geochemical data indicate that the ore fluid has homogenisation temperatures of 165–220 °C, and salinities of 6.6–12 wt.% NaCl equiv., and that the ore-forming fluids and metals were predominantly derived from the Kunyang Group basement rocks and the evaporite-bearing rocks of the cover strata. Ores were deposited along favourable, specific ore-controlling structures. The new laboratory and field studies indicate that the Huize Zn–Pb–(Ag) district is not a carbonate-replacement deposit containing massive sulphides, but rather the deposits can be designated as deformed, carbonate-hosted, MVT-type deposits. Detailed study of the deposits has provided new clues to the localisation of concealed orebodies in the Huize Zn–Pb–(Ag) district and of the potential for similar carbonate-hosted sulphide deposits elsewhere in NE Yunnan Province, as well as the Sichuan–Yunnan–Guizhou Zn–Pb–(Ag) metallogenic region.  相似文献   

8.
Metamorphic remobilization of arsenopyrite-rich ores is a globally important process which can lead to significant concentrations of gold. In order to understand this and related processes, relations of sulphur isotopes can give a number of important clues. To resolve such relations in detail, we have successfully calibrated and applied a laser combustion system for in situ analysis of sulphur isotopic compositions of arsenopyrite. Experimental calibration of the laser fractionation factor (+0.4‰) was obtained by using compositionally and isotopically homogeneous natural samples from ore deposits at Boliden (Sweden) and Freiberg (Germany); subsequent to detailed microscopic study, the S isotope ratios of these samples were measured by conventional and laser combustion techniques.The present application to different types of arsenopyrite in the Palaeoproterozoic metamorphosed VHMS ores of the Boliden Au–Cu–As deposit, Skellefte district, northern Sweden, shows that the sulphur isotope composition of arsenopyrite is essentially unmodified during medium-grade metamorphic recrystallization and remobilization. Here, massive arsenopyrite ore is crosscut by later veins that carry a complex quartz–sulphosalt–sulphide assemblage. The latter ore type is markedly Au-rich compared to the host ore, and thus of significant economic interest. We find that both ore types exhibit very similar sulphur isotope compositions, ca. +2‰ to +3‰ (V-CDT), which is similar to most massive sulphide deposits in the Skellefte district. Thus, the crosscutting Au-rich vein ore has inherited the sulphur isotope composition from sulphur liberated by metamorphic reactions affecting the massive ore, and most likely also inherited the Au through this mechanism. The latter finding clearly has important implications both for the general discussion on, and the prospecting for, similar high-grade Au ores in this world-class mining region.  相似文献   

9.
Geochemically anomalous, pyritic sediments occur directly above a Mid Silurian unconformity in the Quidong area of southeastern New South Wales. The composition of these sediments reflects derivation from a mixture of: (a) feldspar- and mica-depleted detritus reworked from underlying quartz-rich flysch; (b) Mg-rich clay or chlorite precipitated from hydrothermal exhalations; and (c) pyrite formed by reaction of iron in clays or oxides with reduced sulphur derived largely from sea-water sulphate and possibly a magmatic source. Three types of base metal sulphide mineralisation occur at Quidong including: (a) weak syngenetic concentrations in the pyritic sediments; (b) stratabound and fault-controlled bodies of massive sulphides hosted by the pyritic sediments and containing higher grade Pb, Zn and Cu; and (c) small vein and cavity fillings of galena, barite and other minor sulphides in overlying limestones. All types of mineralisation are related to hydrothermal activity which occurred during and after deposition of the pyritic facies. The geochemistry of the immediately underlying basement rocks and Pb isotope data indicate that the source of the metal-bearing fluids was deeper in the crust and probably related to widespread partial melting and magmatic processes. The sulphidic sediments and stratabound sulphide deposits represent syngenetic-epigenetic, sediment hosted mineralisation developed in a shallow marine environment, distal from major volcanic centers. This style of mineralisation has not previously been described from the region. It has some similarities to the Irish-Alpine type spectrum of deposits best known in Europe.  相似文献   

10.
The principal copper deposits associated with Upper Creataceous — Laramian calc-alkaline volcano-plutonic complexes in the Bor district are classified as follows: Volcanogenic massive sulphide deposits are situated in andesitic volcanics, and are composed of pyrite and copper sulphides. Multistage deposition of mineral associations in this area was controlled mainly by secondary boiling of hydrothermal fluids rich in sulphur. Apart from cupriferous pyrite deposits, volcanogenic massive polymetallic deposits, containing a pyritic ZnCu+Pb association, have been found recently in hydrothermally altered dacite- and esite pyroclastics. Porphyry copper deposits are mainly situated in volcanic piles related to subvolcanic intrusions and/or hypabyssal plutons. Some porphyry copper deposits occur in the same structures with massive sulphide orebodies, lying above the porphyry copper system. Conglomerate-type ores consisting of clasts of massive sulphide in an andesitic pile have been discovered recently.  相似文献   

11.
Sedimentary rock-hosted Au deposits in the Dian–Qian–Gui area in southwest China are hosted in Paleozoic and early Mesozoic sedimentary rocks along the southwest margin of the Yangtze (South China) Precambrian craton. Most deposits have characteristics similar to Carlin-type Au deposits and are spatially associated, on a regional scale, with deposits of coal, Sb, barite, As, Tl, and Hg. Sedimentary rock-hosted Au deposits are disseminated stratabound and(or) structurally controlled. The deposits have many similar characteristics, particularly mineralogy, geochemistry, host rock, and structural control. Most deposits are associated with structural domes, stratabound breccia bodies, unconformity surfaces or intense brittle–ductile deformation zones, such as the Youjiang fault system. Typical characteristics include impure carbonate rock or calcareous and carbonaceous host rock that contains disseminated pyrite, marcasite, and arsenopyrite—usually with μm-sized Au, commonly in As-rich rims of pyrite and in disseminations. Late realgar, orpiment, stibnite, and Hg minerals are spatially associated with earlier forming sulfide minerals. Minor base–metal sulfides, such as galena, sphalerite, chalcopyrite, and Pb–Sb–As–sulphosalts also are present. The rocks locally are silicified and altered to sericite–clay (illite). Rocks and(or) stream-sediment geochemical signatures typically include elevated concentrations of As, Sb, Hg, Tl, and Ba. A general lack of igneous rocks in the Dian–Qian–Gui area implies non-pluton-related, ore forming processes. Some deposits contain evidence that sources of the metal may have originated in carbonaceous parts of the sedimentary pile or other sedimentary or volcanic horizons. This genetic process may be associated with formation and mobilization of petroleum and Hg in the region and may also be related to As-, Au-, and Tl-bearing coal horizons. Many deposits also contain textures and features indicative of strong structural control by tectonic domes or shear zones and also suggest syndeformational ore deposition, possibly related to the Youjiang fault system. Several sedimentary rock-hosted Au deposits in the Dian–Qian–Gui area also are of the red earth-type and Au grades have been concentrated and enhanced during episodes of deep weathering.  相似文献   

12.
The Late Devonian-Early Carboniferous (Dinantian) within the Western Hercynides is marked by the formation of volcanic-hosted massive sulphide deposits: Chessy and Chizeuil in the Brévenne and Somme successions of the French Massif Central; Bodennec and La Porte-aux-Moines in the Châteaulin Basin of the French Armorican Massif; Rio Tinto, Neves-Corvo, Tharsis, etc., in the Volcano-Sedimentary formation of the Iberian Pyrite Belt; and Ketara, Draa Sfar and Hajar in the Jebilet-Guemassa district of the Moroccan Southern Meseta. Although these deposits show a slightly diachronous emplacement in response to a progressive migration of the metalliferous event from Late Devonian in France to Dinantian in Morocco, it is nevertheless possible to define an overall metalliferous ‘‘peak” around 350 Ma. The mineralization of the Armorican, Iberian and Moroccan sectors took place in epicontinental domains of the outer zone of the Hercynian belt, whereas that of the northeastern Massif Central occurred within the inner zone of the belt. This difference is registered by variations both in the geochemical characteristics of the ores (Sn in the outer zone and Mo-Ni in the inner zone) and in their lead isotopic signatures (clear mantle participation exclusively in the inner zone). In many cases the ores appear to be closely related to the felsic member of a bimodal magmatic association, although the massive sulphide deposits in the outer zone are more commonly associated with sedimentary rocks whereas those in the inner zone are hosted by felsic volcanic rocks. Another feature that should be noted is that the host sequences of the massive sulphide deposits commonly seem to be underlain by chaotic formations (notably with olistoliths) reflecting the beginning of Hercynian orogenic activity in the outer zone. It can be concluded that the peak mineralization took place within tensional domains developed during a period of plate convergence, and that it occurred around 350 Ma after a major period of Devonian compression but before the Carboniferous continental closure.  相似文献   

13.
The Ortaklar VMS deposit is hosted in the Koçali Complex consisting of basalts and deep sea pelagic sediments, which formed by rifting and continental break-up of the southern Neotethyan in Late Triassic. The basalts are of NMORB-type without notable crustal contamination. From the surface to depth, the Ortaklar deposit consists of a gossan zone, a thick massive ore zone and a poorly developed stockwork zone. Primary mineralisation is characterised by distinctive facies including sulphide breccias (proximal), graded beds (distal), stockworks and chimney fragments. Ore mineral abundances decrease in the order of pyrite, magnetite, chalcopyrite, and sphalerite. Two distinct phases of mineralisation, massive magnetite and massive sulphide, are present in the Ortaklar deposit. Textural evidence (e.g., magnetite replacing sulphides) and the spatial relationships with the host rocks indicate that magnetite and sulphide minerals were generated in different stages. The transition from sulphide to magnetite mineralisation is interpreted to relate to variation in H2S content of ore fluids. The 1st stage massive sulphide ore might have formed by early hydrothermal fluids rich in Fe and H2S. The 2nd stage massive magnetite might have formed by later neutral hydrothermal fluids rich in Fe but poor in H2S, replacing the pre-existing sulphide ore.The alteration patterns, mineral paragenesis, lithological features (massive ore-stockwork ore-gossan) of the Ortaklar deposit together with its trace elements, Cu-Pb-Zn-Au-Ag and REE signatures are all consistent with a Cyprus-type VMS system. The δ34S values in pyrite and chalcopyrite samples range from 2.6 to 5.7‰, indicating that the hydrothermal fluids were associated with sub-seafloor igneous activity, typical of Cyprus-type VMS deposits. However, magnetite formed later than sulphide minerals in the Ortaklar deposit, contrasting with typical Cyprus-type VMS deposits where magnetite generally occurs in lower sections. Consequently, although the Ortaklar deposit generally conforms to Cyprus-type deposits, it is distinguished from them by its late stage and high magnetite concentration. Thus, the Ortaklar deposit is thought to be an exceptional and perhaps unique Cyprus-type VMS deposit.  相似文献   

14.
Auriferous quartz pebble conglomerates (QPC) formed during Tertiary sedimentary recycling in the Waimumu district, Southland, New Zealand. These sediments contain fine-grained gold of detrital origin with abundant surface textures and gold-forms associated with authigenic gold remobilisation. Most authigenic gold contains no detectable silver and occurs as overgrowths on detrital Au–Ag and Au–Ag–Hg alloys that contain up to 13 wt.% Ag, and 9 wt.% Hg. Fine-grained Au–Ag and Au–Ag–Hg alloys are compositionally heterogeneous, exhibiting both well-defined silver-depleted and silver-enriched rims. Rare coarse Au–Ag alloy is intergrown with quartz and is homogenous. Discrete grains of authigenic, porous, sheet-like gold occur in carbonaceous mudstone within a QPC sequence. Some QPC contain abundant sulphide minerals. Some of these sulphides (pyrite and arsenopyrite) are of long-distance detrital origin, presumably from the Otago Schist, whereas the bulk of the sulphide suite is marcasite of variably transported diagenetic origin, derived from the erosion of QPC and underlying Tertiary sediments. There has also been authigenic deposition of sulphide minerals in the QPC themselves. These diagenetic sulphides include framboidal and anhedral marcasite, and framboidal and euhedral pyrite. Sulphur isotope data for the sulphide minerals range from − 45‰ to + 18‰ (relative to VCDT). Sulphur isotope data for euhedral detrital pyrite and arsenopyrite range from − 9‰ to − 1‰ and are most likely derived from the Otago Schist to the north. Both framboidal and anhedral marcasite have lower values (< − 20‰) reflecting microbial sulphate reduction as a source for the precursor hydrogen sulphide. Anhedral marcasite contains elevated concentrations of Ni, Co, As and Cr, commonly with compositional banding of these metals.Both the gold and diagenetic sulphides from the Belle-Brook QPC are compositionally similar to gold and sulphides from Archaean QPC. Porous, sheet-like authigenic gold is morphologically similar to gold associated with carbonaceous material in the Witwatersrand. In addition, Southland marcasite textures resemble the rounded and banded pyrite in Witwatersrand QPC placers. There is abundant evidence from these Tertiary QPC in southern New Zealand for sedimentary transport of sulphide minerals and post-depositional sulphide mineralisation in the surficial environment despite an oxygen-rich atmosphere. These young deposits thus provide an example of authigenic gold and sulphide textures formed during diagenesis in unmetamorphosed placers. Many of these textures are similar to those commonly ascribed to metamorphic processes in Archaean auriferous QPC.  相似文献   

15.
The Yueshan mineral belt is geotectonically located at the centre of the Changjiang deep fracture zone or depression of the lower Yangtze platform. Two main types of ore deposits occur in the Yueshan orefield: Cu–Au–(Fe) skarn deposits and Cu–Mo–Au–(Pb–Zn) hydrothermal vein-type deposits. Almost all deposits of economic interest are concentrated within and around the eastern and northern branches of the Yueshan dioritic intrusion. In the vicinity of the Zongpu and Wuhen intrusions, there are many Cu–Pb–Zn–Au–(S) vein-type and a few Cu–Fe–(Au) skarn-type occurrences.Fluid inclusion studies show that the ore-forming fluids are characterised by a Cl−(S)–Na+–K+ chemical association. Hydrothermal activity associated with the above two deposit types was related to the Yueshan intrusion. The fluid salinity was high during the mineralisation processes and the fluid also underwent boiling and mixed with meteoric water. In comparison, the hydrothermal activity related to the Zongpu and Wuhen intrusions was characterised by low salinity fluids. Chlorine and sulphur species played an important role in the transport of ore-forming components.Hydrogen- and oxygen-isotope data also suggest that the ore-forming fluids in the Yueshan mineral belt consisted of magmatic water, mixed in various proportions with meteoric water. The enrichment of ore-forming components in the magmatic waters resulted from fluid–melt partitioning. The ore fluids of magmatic origin formed large Cu–Au deposits, whereas ore fluids of mixed magmatic-meteoric origin formed small- to medium-sized deposits.The sulphur isotopic composition of the skarn- and vein-type deposits varies from − 11.3‰ to + 19.2‰ and from + 4.2‰ to + 10.0‰, respectively. These variations do not appear to have been resulted from changes of physicochemical conditions, rather due to compositional variation of sulphur at the source(s) and by water–rock interaction. Complex water–rock interaction between the ore-bearing magmatic fluids and sedimentary wall rocks was responsible for sulphur mixing. Lead and silicon isotopic compositions of the two deposit types and host rocks provide similar indications for the sources and evolution of the ore-forming fluids.Hydrodynamic calculations show that magmatic ore-forming fluids were channelled upwards into faults, fractures and porous media with velocities of 1.4 m/s, 9.8 × 10− 1 to 9.8 × 10− 7 m/s and 3.6 × 10− 7 to 4.6 × 10− 7 m/s, respectively. A decrease of fluid migration velocity in porous media or tiny fractures in the contact zones between the intrusive rocks and the Triassic sedimentary rocks led to the deposition of the ore-forming components. The major species responsible for Cu transport are deduced to have been CuCl, CuCl2−, CuCl32− and CuClOH, whereas Au was transported as Au2(HS)2S2−, Au(HS)2−, AuHS and AuH3SiO4 complexes. Cooling and a decrease in chloride ion concentration caused by fluid boiling and mixing were the principal causes of Cu deposition. Gold deposition was related to decrease of pH, total sulphur concentration and fO2, which resulted from fluid boiling and mixing.Geological and geochemical characteristics of the two deposit types in the Yueshan mineral belt suggest that there is a close genetic relationship with the dioritic magmatism. Geochronological data show that the magmatic activity and the mineralisation took place between 130 and 136 Ma and represent a continuous process during the Yanshanian time. The cooling of the intrusions and the mineralisation event might have lasted about 6 Ma. The cooling rate of the magmatic intrusions was 80 to 120 °C my− 1, which permitted sufficient heat supply by magma to the ore-forming system.  相似文献   

16.
The Western Tharsis disseminated Cu–Au orebody, which occurs within the Cambrian Mt Read Volcanics of Western Tasmania, is surrounded by a pyritic halo that extends 100–200 m stratigraphically above and below the ore zone. Although this halo extends laterally along the same stratigraphic position to the south, it probably closes off to the north based on limited surface and drill hole data. The ore zone is characterized by extreme enrichment (the enrichments and depletions referred to herein are relative to background; these have not been established using mass balance techniques) in As, Bi, Ce, Cu, Mo, Ni, S and Se; with the exception of Mo, these elements are also enriched, but at a much lower level, in the pyrite halo.Pronounced depletion in K, Cs and Mg occurs in 20–30 m wide stratiform zones that flank the orebody on both sides within the pyritic halo. These anomalies and depletions in Be, Ga, Rb, Y, MREE and HREE are associated with a pyrophyllite-bearing alteration zone that wraps around the main pyrite–chalcopyrite-bearing ore zone. This zone is also characterized by positive Eu anomalies which persist up to 150 m both into the hanging wall and footwall of the orebody. The depletion of these elements is consistent with the advanced argillic alteration assemblage developed about acid-sulfate Cu–Au deposits.The pyrite halo is surrounded by a peripheral carbonate halo which is highly enriched in C, CaO and MnO, and weakly enriched in Zn and Tl. Zinc and Tl are most enriched in the upper 100–150 m of the stratigraphically lower halo. In the stratigraphically upper halo, Zn and Tl values are anomalously high but erratic.Barium and Sr enrichment, although mainly restricted to the pyrite halo, extends into the stratigraphically lower carbonate halo by up to 100 m. A Na depletion anomaly extends from 150 m below the orebody and to at least the Owen contact (i.e. ≥400 m)in the hanging wall.The dispersion patterns observed at Western Tharsis are quite unlike those of Zn–Pb-rich volcanic-hosted massive sulfide (VHMS) deposits in western Tasmania. Rather, the dispersion patterns observed at Western Tharsis are more akin to those surrounding porphyry Cu deposits and related acid-sulfate Cu–Au deposits.  相似文献   

17.
Australian Proterozoic gold-producing deposits, emplaced mainly at 1.55–2.00 Ga, are divided into the following categories: (1) iron oxide-dominated, brecciahosted, Cu-U±Au replacement deposits spatially associated with felsic intrusions (273t Au); (2) stratabound Au±Cu-bearing iron formations (152.4t Au); (3) unconformity-style U ±Cu/PGM/Au deposits (53t Au); (4) Iron oxide-dominated Au±Cu mineralisation hosted within elements of ductile deformation (146.7t Au); (5) Broken Hill and volcanic-hosted massive sulphides (150t Au); (6) iron-sulphide-dominated veins and replacement zones spatially related to felsic intrusions (150.7t Au), and (7) iron-sulphide-dominated veins and replacement zones spatially related to elements of regional deformation (159.9t Au). Categories (1) to (4) are mainly confined to Proterozoic rocks, constituting an association in which Au and Cu are commonly present together, with variable amounts of U, Bi, Co, W, Se, Te and REE. Most examples in categories 1–4 fall into either of two groups: Cu-Aumagnetite ±hematite types formed at relatively high temperature (300–450 °C), and Cu-U±Au-hematite types formed at 150–300 °C. We postulate that these ores formed from a common high salinity (15–35 wt. % NaCl equiv.), low total sulphur (aS = 10–3 to 10–2), high fO2 fluid-type, in which metal transport was dominated by chloride-complexing. The most effective method of metal deposition was fluid mixing, achieving a synchronous decrease in fO2 and temperature. This unusual oxidised fluid association was favoured in high heat-flow extensional settings containing oxidised and/or oxidised-evaporitic sedimentary sequences. The intrusion of oxidised fractionated granites, which are commonly temporally associated with metal emplacement, acted in some places to heat and focus basinal fluids, and in others was the ultimate source of metals.  相似文献   

18.
论华南喷流—沉积块状硫化物矿床   总被引：28，自引：1，他引：27  
现代海底喷流－沉积硫化物矿床的发现极大地推动了海底热液成矿理论的发展,也大大地提高了对古代海底喷流块充化物矿术的研究水平。本文指出喷流－沉积是重要的成矿作用,提出喷流－沉积矿床是华南Ｃｕ、Ｐｂ、Ｚｎ、Ｓｎ、Ａｇ、Ａｕ等矿产资源的重要来源,形成了一批超大型矿床,并将华南许多曾被认为属夕卡岩矿床重新确认为喷流－沉积岩床。文章还论述了华南喷流－沉积块状硫化物矿床的特征、分类、时空分布及其成矿特点等问题,提出断裂拗陷带型喷流－沉积块状硫化物矿床是华南具有特色的类型,而陆相断陷盆地中喷流－沉积矿床值得进一步深入研究。  相似文献   

19.
The Rammelsberg polymetallic massive sulphide deposit was the basis of mining activity for nearly 1000 y before finally closing in 1988. The deposit is hosted by Middle Devonian pelitic sediments in the Rhenohercynian terrane of the Variscan Orogen. The deposit consists of two main orebodies that have been intensely deformed. Deformation obscures the original depositional relationships, but the regional setting as well as the geochemistry and mineralogy of the mineralisation display many characteristics of the SHMS (sediment-hosted massive sulphide) class of ore deposits. Rammelsberg is briefly compared to the other massive sulphide deposits in the European Variscan, including Meggen and those deposits in the Iberian Pyrite Belt. Received: 28 September 1998 / Accepted: 5 January 1999  相似文献   

20.
The mineralisation potential of Palaeoproterozoic strata from the central Gawler Craton, South Australia, is poorly known. This study defines the timing of Zn-rich skarn formation within Palaeoproterozoic calcsilicate and highlights this as a new mineralisation style for the Gawler Craton. Sulphides within the garnet–diopside skarn in the No. 17 Bore Prospect are predominantly in the form of sphalerite, associated with galena, minor chalcopyrite, pyrrhotite and pyrite. Sulphide is present in disseminated form and as a coarse-grained sulphide within a sericite-rich cavity-fill. Mineralisation is inferred to have formed at 1710 ± 16 Ma through a Sm–Nd isochron from garnet and diopside aliquots. A weakly mineralised and altered granite immediately below the calcsilicate skarn crystallised at 1729 ± 13 Ma (LA-ICPMS U–Pb zircon), within error of the skarn mineralisation. The skarn is interpreted to have formed through the initiation of fluid circulation as a result of high-level granite emplacement within the Palaeoproterozoic strata. Exploration for skarn Zn–Pb deposits such as the No. 17 Bore Prospect is assisted by their geophysical properties.  相似文献   

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