Cu, Mn, and Ag mineralization in the Quebrada Marquesa Quadrangle, Chile: the Talcuna and Arqueros districts

The Quebrada Marquesa Quadrangle in Chile exhibits a series of mineralizations comprising manto-type manganese and copper deposits of Lower Cretaceous age, and copper and silver veins of Tertiary age. The deposits are hosted by volcanic and volcaniclastic units of the Arqueros (Hauterivian-Barremian) and Quebrada Marquesa (Barremian-Albian) Formations. Three episodes of manganese mineralization (Mn_1-3) are recognized within the study area. Hydrothermal activity leading to episodes 1 and 3 was of minor importance, while the second one (Mn₂) gave rise to major manto-type deposits of both manganese and copper in the Talcuna mining district. Extensional faulting during Tertiary time resulted in block faulting and the unroofing of the oldest andesitic volcanics and marine sediments (Arqueros Formation). This episode was accompanied by magmatic and hydrothermal activity leading to vein formation in the Arqueros (Ag) and Talcuna (Cu) districts. The latter veins cross-cut the previous manto-type copper deposits. Ore mineralogy is similar in both styles of mineralization (manto- and vein-type) and consists mainly of chalcopyrite and bornite, with variable amounts of galena, tetrahedrite (vein-related), chalcocite, sphalerite, pyrite, hematite, digenite and covellite. Alteration processes at Talcuna can be divided into two categories, those related to the Lower Cretaceous manto-type episode (LK alteration: chlorite-epidote-calcite-albite, prehnite, zeolite), and those associated with the locally mineralized normal faults of Tertiary age (Tt alteration: chlorite-calcite, sericite). The Arqueros silver veins display an ore mineralogy consisting of arquerite, argentite, native silver, polybasite, cerargyrite and pyrargyrite-proustite; associated alteration includes strong chloritization of the country rock. The manto-type deposits formed from fluids of salinity between 11 and 19 wt.% NaCl equivalent and temperatures between 120 and 205 °C. Mineralizing fluids during the vein-type stage circulated at lower temperatures, between 70 and 170 °C, with salinity values in a wide range from 3 to 27 wt.% NaCl equivalent. This distribution of salinities is interpreted as the result of the complex interplay of two different processes: boiling and fluid mixing; the former is considered to control the major mineralogical, textural and fluid inclusion features of the vein-type deposits. We suggest that the Lower Cretaceous mineralization (manto-type stage) developed in response to widespread hydrothermal activity (geothermal field-type) involving basinal brines. Received: 18 July 1997 / Accepted: 28 January 1998     

黔西南卡林型金矿床中固体有机物质的有机岩石学研究

固体有机物质保留了金属矿床成矿过程的重要信息。本文以黔西南烂泥沟和戈塘两个典型金矿床为例,系统研究了其中的固体有机物质的有机岩石学特征,并探讨了固体有机质与金矿化的关系。烂泥沟金矿固体有机质由原生煤系有机质和异源焦沥青组成。煤系有机质为原生有机质,与成岩黄铁矿关系密切,没有直接参与热液成矿作用。焦沥青沿石英脉壁粘附或在细脉和纹层中呈带状分布,是热液成矿期原油热液蚀变的产物,原油搬运Au,遭受热液蚀变并参与热化学还原,导致Au 的释放和沉淀。戈塘金矿床中有机质主要是煤系有机质碎屑,与上覆的含煤层有成因联系。这些有机质在热液过程中遭受热液蚀变,还原硫酸盐,为硫化物的沉淀提供还原硫。     

Re-Os-Isotope Systematics of Sulfides from Base-Metal Porphyry and Manto-Type Mineralization in Chile

Chile is a major world producer of copper, most of which occurs in base-metal porphyry and in manto deposits. A fundamental difference between these two types of deposits is the relative importance of intrusions spatially associated with the mineralization. The porphyry deposits are set within Mesozoic to Tertiary intrusive complexes. The manto-type deposits are restricted to volcanic and volcano-sedimentary sequences of Middle-Late Jurassic, Early Cretaceous, Late Cretaceous, and Early Tertiary times. Large intrusive centers are not spatially associated with these deposits, although minor intrusions are common. A central question in the metallogenesis of these deposits is the source of ore-forming components, in particular the ore metals. Initial 187Os/188Os isotopic data from sulfides from the El Teniente, La Disputada, and Andacollo base-metal porphyry deposits range from 0.19 to 1. These data indicate that the Os (and, by inference, Cu) is mostly crustally derived, since it is more radiogenic than that of the mantle, which has a ¹⁸⁷Os/¹⁸⁶Os ratio of ～0.12. The isotopie data for El Soldado, which is an important example of manto-type mineralization, are significantly more radiogenic, with ¹⁸⁷Os/¹⁸⁸Os ratios greater than 3. These radiogenic values require that the Os come from a crustal reservoir with a high Re/Os ratio, such as black shales. The Os-isotopic data indicate that the source for these two types of base-metal deposits is different, but that both Os reservoirs reside in the crust.     

Extremely negative and inhomogeneous sulfur isotope signatures in Cretaceous Chilean manto-type Cu–(Ag) deposits,Coastal Range of central Chile

Chilean manto-type (CMT) Cu(–Ag) hydrothermal deposits share a characteristic association of volcano-sedimentary Jurassic to Lower Cretaceous host rocks, style of mineralization, ore and associated mineralogy and geochemistry, with ore grades typically > 1%Cu, that make this family of deposits significant and interesting, both academically and economically. Although often stratabound, geological evidence supports an epigenetic origin for these deposits. We present a detailed stable isotope study of La Serena and Melipilla–Naltahua Lower Cretaceous deposits, central Chile, which reveals extremely negative δ³⁴S values, to − 50‰, which are among the lowest values found in any ore deposit. In addition, the range of δ³⁴S values from sulfides in the two areas is very wide: − 38.3 to − 6.9‰ in La Serena, and − 50.4 to − 0.6‰ in Melipilla–Naltahua. These new data significantly extended the reported range of δ³⁴S data for CMT deposits. Co-existing sulfates range from 7.9 to 14.3‰, and are exclusive to La Serena deposit. The wide sulfide isotopic range occurs at deposit and hand specimen scale, and suggests a polygenic sulfur source for these deposits, where bacteriogenic sulfide dominates. While sulfur isotope data for the bulk of Jurassic CMT deposits, northern Chile, suggests a predominant magmatic source in their origin (mean = − 2.7 ± 1.9‰, 1σ), contributions of a magmatic component is only likely to be involved at Melipilla–Naltahua deposit.The δ¹³C values obtained for calcites associated with the mineralization range from − 20.1 to 0.2‰ also suggesting polygenic carbon sources, with the likely strong involvement of degradation of organic matter and leaching of limestone.Two different genetic models, with involvement of hydrocarbon, are proposed for both areas. For Melipilla–Naltahua, a two-step model can be developed as follows: 1) Framboidal pyrite growth, with very low δ³⁴S, formed by bacterial sulfate reduction in an open system, and with diagenetic degradation of oil-related brines, leaving pyrobitumen. 2) Cu-bearing stage, replacing of framboidal pyrite, inheriting depleted sulfur as low as − 50.4‰, together with sulfides directly precipitated from a hydrothermal fluid with δ³⁴S close to 0‰. For La Serena, a single step model fits best, without framboidal pyrite generation. Cu-bearing sulfides were precipitated mainly in veins where Cu plus base metal-bearing hydrothermal fluids mixed with H₂S generated by bacterial sulfate reduction in the host rocks. Isotopic evidence clearly illustrates that bacterial activity, perhaps enhanced by hydrothermal activity, was fed by hydrocarbon brines and sulfate remobilized from continental evaporites. It is possible that variable ecological conditions led to different extents of isotopic fractionation, adding to the typical sulfur isotopic heterogeneity of such bacterial systems. For both areas, the Cu-bearing stage occurred during the peak to waning stages of the very low-grade metamorphism that affected the Lower Cretaceous sequence.     

西天山金、铜矿地质特征简述

西天山是我国古生代造山带重要的金、铜矿成矿单元之一,具有Au、Cu地球化学场.各种地球物理场也显示具有良好的金、铜矿成矿地质背景.金、铜矿主要生成于海西期的构造岩浆地质热事件中,形成了浅成低温热液型和韧性剪切带型金矿以及海底火山喷气热水沉积型、矽卡岩型、斑岩型、陆相火山热液充填型铜矿.可划分出赛里木铜金成矿带、吐拉苏也里莫墩金成矿带、察布查尔铜成矿带及胜利达坂金成矿带.主要矿床有阿希金矿、望峰金矿、喇嘛苏铜矿和预须开普台铜矿.     

Genetic Aspects of the Manto-type Copper Deposits Based on Geochemical Studies of North Chilean Deposits

Recent studies on mineralogy, geochronology, fluid inclusion and stable isotope (Pb, Os, S, C, O, Sr) characteristics were reviewed to determine constraints for genetic models of the Chilean manto‐type copper deposits. The Chilean manto‐type deposits are divided into the two geologic categories of the northern areas (Arica–Iquique, Tocopilla–Taltal) and the central areas (Copiapó, La Serena, Santiago). The former is distributed in the coastal range composed of Jurassic andesite‐dominated volcano‐sedimentary piles and younger plutonic intrusions, and yields chalcocite (‐digenite) and bornite as the principal hypogene copper sulfides. The latter is hosted mostly in Lower Cretaceous volcano‐sedimentary sequences, and has chalcopyrite‐rich mineral associations. The fluid inclusion data indicate that the primary copper mineralization was commonly generated in the temperature range 150–360°C under low‐pressure conditions near the boiling curve, mediated with relatively saline brines. Generally, homogeneous Pb and S isotope compositions for primary copper minerals imply direct magma source or leaching of igneous rocks. Pb and Os isotope data published for some deposits, however, suggest that ore‐forming metals were derived mainly from the volcano‐sedimentary host rocks. The noticeably negative isotope ratios of primary sulfide sulfur and hydrothermal calcite carbon of some central area deposits indicate influx of sedimentary rock components, and the high ⁸⁷Sr/⁸⁶Sr initial ratios of hydrothermal calcite from the Tocopilla–Taltal area deposits imply contribution of the contemporaneous seawater or marine carbonates. These isotopic constraints imply a formation mechanism in which the Chilean manto‐type copper deposits formed epigenetically in the process of hydrothermal interaction of non‐magmatic surface‐derived brine with the volcano‐sedimentary host rocks, which is inferred to have been induced by a deep‐seated plutonic complex as the possible heat source.     

Alteration patterns and structural controls of the El Espino IOCG mining district,Chile

The El Espino IOCG mining district is characterized by several mineralized bodies the largest of which is the El Espino deposit, which has an estimated geologic resource of 123 Mt at 0.66 % Cu and 0.24 g/t Au. Mineralized bodies are distributed in a 7?×?10 km² area throughout a 1,000-m vertical section. They range from single veins to stockworks and breccias to manto-type deposits. The ore bodies are hosted primarily by volcanic, volcaniclastic, and sedimentary rocks of the Early Cretaceous Arqueros and Quebrada Marquesa formations, with a few mineralized zones within Late Cretaceous dioritic intrusions. The fault and vein architecture shows that El Espino IOCG system was localized within a dilatational jog along a major transtensional dextral fault system. Sodic alteration (albite) is the most extensive style of alteration in the district, and it is bounded by major NS–NNE trending faults. Sodic–calcic (epidote–albite) alteration occurs at deep to medium elevations (1,000–500 m) and grades inward into calcic alteration. Calcic alteration surrounds dioritic intrusions of the Llahuin plutonic suite. Significant iron oxides are associated with later calcic alteration associations (actinolite–epidote–hematite). The upper portions of the alteration system (0–500 m) display hydrolytic alteration associations with abundant hematite. Hydrolytic veins are feeders to zones of manto-type alteration and mineralization within favorable volcano-sedimentary lithologies that formed El Espino deposit. Sulfides are largely confined to calcic and hydrolytic alteration associations. Hydrothermal fluids responsible for hematite and sulfide mineralization had salinities between 32 and 34 wt% NaCl_eq and temperature of approximately 425 °C at an estimated depth of 3–4 km. Geochronological U–Pb and ⁴⁰Ar/³⁹Ar data indicate that hydrothermal alteration was coeval with magmatic intrusive activity. One particular dioritic intrusion (88.5 Ma) preceded the calcic stage (88.4 Ma), which was accompanied by iron oxide copper and gold mineralization. Hydrolytic alteration, related to economic iron oxide copper and gold mineralization, came immediately after at 87.9 Ma.     

Proterozoic copper deposits in NW Queensland,Australia: Sulfur isotopic data

Sulfur isotopic disequilibrium is commonly observed between associated pyrite and copper sulfides in NW Queensland. A sulfur isotopic study of copper mineralization in dolomites at Paradise Valley and arenites at Mammoth has allowed the significance of such disequilibrium to be evaluated. Copper mineralization at Paradise Valley is characterized by a greater enrichment in ³⁴S, with δ³⁴S values often greater than +30‰, for both copper sulfides and associated syngenetic/diagneetic pyrite. At Mammoth, copper sulfides have isotopic compositions (δ³⁴S=?15.9 to ?0.3‰) transitional between disseminated syngenetic/diagenetic pyrite (δ³⁴S=?5.7 to ?1.7‰) and epigenetic vein pyrite (δ³⁴S=?17.9 to ?7.1‰) suggesting progressive reaction and replacement of syngenetic/diagenetic pyrite by a copper-bearing mineralizing fluid under oxidizing conditions. The isotopic data, within the constraints imposed by geological and geochemical factors, support a model of reaction between copper-bearing mineralizing fluids and pre-existing syngenetic/diagenetic pyrite for both the carbonate- and arenite-hosted deposits.     

A magmatic source of hydrothermal sulfur for the Prominent Hill deposit and associated prospects in the Olympic iron oxide copper-gold (IOCG) province of South Australia

The Prominent Hill deposit is a world-class iron oxide copper–gold (IOCG) deposit in South Australia, characterized by a high Cu/S ratio of the dominant Cu-(Fe) sulfides hosted by hematite breccias. It contains a total resource of 278 Mt of ore at 0.98% Cu and 0.75 g/t Au. Prominent Hill is one of several IOCG deposits and numerous prospects in the Olympic IOCG province that are temporally associated with the 1603–1575 Ma Gawler Range Volcanics, a large igneous province including co-magmatic granitoid intrusions of the Hiltaba Suite. Globally, IOCG deposits share many similar features in terms of their geological environment and mineral association. However, it is not yet clear whether sulfur and copper originate from the same source rocks and which hydrothermal redox processes created the characteristic iron oxide enrichment. Highly variable sulfur isotope compositions of sulfides and sulfates in IOCG deposits have previously been interpreted in terms of diverse sulfur sources that may include contributions from magmatic, sedimentary, seawater or evaporitic sulfur. In order to test these alternatives, we performed a detailed sulfur isotope study of Cu-(Fe) sulfides from Prominent Hill and IOCG prospects nearby. The Prominent Hill deposit shows a wide range in δ³⁴S_V-CDT between − 33.5‰ and 29.9‰ for Cu-(Fe) sulfides, and a narrower range of 4.3‰ to 15.8‰ for barite. Iron sulfides (pyrite, pyrrhotite) show a narrow range in sulfur isotope composition, whereas Cu-bearing sulfides show a much wider range, and more negative δ³⁴S_V-CDT values on average. We propose a two-stage sulfide mineralization model for the IOCG system in the Prominent Hill area, in which all hydrothermal sulfur is ultimately derived from a magmatic source that had a composition of 4.4 ± 2‰. The diversity in sulfur isotope composition can be produced by different fluid evolution pathways along reducing or oxidizing trajectories. A reduced sulfur evolution pathway is responsible for stage I mineralization, when intrusion-derived magmatic-hydrothermal fluids produced early pyrite and minor chalcopyrite at Prominent Hill, and iron ± copper sulfides in regional magnetite skarns and in some pervasively altered volcanic rocks of the Gawler Range Volcanics. Shallow-venting magmatic-hydrothermal fluids and subaerial volcanic gases that became completely oxidized by reaction with atmospheric oxygen produced sulfate and sulfuric acid with a sulfur isotope composition equal to their magmatic source. This highly oxidized ore fluid probably consisted dominantly of water from the hydrosphere, but contained magmatic solute components, notably sulfate, acidity and Cu. Sulfate reduction produced hydrothermal Cu sulfides with a wide range in sulfur isotope compositions from very negative to moderately positive values. Partial reaction of the Cu-rich stage II fluid with earlier stage I sulfides resulted in mixing of sulfur derived from sulfate reduction and from sulfides deposited during stage I. Modeling of the sulfur isotope fractionation processes in response to reducing and oxidizing pathways demonstrates that the entire spectrum of sulfur isotope data from stage I and stage II mineralization can be explained with a single, ultimately magmatic sulfur source. Such a magmatic sulfur source is also adequate to explain the complete spectrum of sulfur isotope data of other IOCG prospects and deposits in the Olympic province, including Olympic Dam. The results of our study challenge the conventional model that suggests the requirement of multiple and compositionally diverse sulfur sources in hematite-breccia hosted IOCG style mineralization.     

Origin of the Oligocene Tuolangla porphyry-skarn Cu-W-Mo deposit in Lhasa terrane,southern Tibet

Although some porphyry-skarn deposits occur in post-collisional extensional settings, the post-collisional deposits remain poorly understood. Here the authors describe the igneous geology, and mineralization history of Tuolangla, a newly-discovered porphyry-skarn Cu-W-Mo deposit in southern Tibet that belongs to the post-collisional class. The deposit is associated with Lower Cretaceous Bima Formation. It was intruded by granodiorite porphyry intrusions at about 23.1 Ma. Field investigation indicated that mineralization is spatially and temporally associated with granodiorite porphyry. Molybdenite yielded a Re-Os weighted mean age of 23.5 ± 0.3 Ma and is considered to represent the age of skarn mineralization at the deposit. The δ³⁴S values of sulfides, concentrated in a range between 0.6‰ to 3.4‰, show that the sulfur has a homogeneous source with characteristics of magmatic sulfur. The Pb isotopic compositions of sulfides indicate that ore-forming metal materials were derived from the mantle and ancient crust. The granodiorite porphyry displays high SiO₂ (68.78%–69.75%) and K₂O (3.40%–3.56%) contents, and relatively lower Cr (2.4×10^-6–4.09×10^-6), Ni (2.79×10^-6–3.58×10^-6) contents, and positive ε_Hf(t) values (7.7–12.9) indicating that the mineralization porphyry was derived from the partial melting of juvenile lower crust. The Tuolangla deposit is located in the central part of Zedang terrane. This terrane was once considered an ancient terrane. This terrane is in tectonic contact with Cretaceous ophiolitic rocks to its south and Mesozoic continental margin arc volcanics and intrusions of the Gangdese batholith of the Lhasa terrane to its north. Thus, the authors proposed that the Oligocene porphyry skarn Cu-W-Mo mineralization is probably associated with the Zedang terrane. This finding may clarify why the Oligocene (about 23 Ma) deposits are found only in the Zedang area and why mineralization types of the Oligocene mineralization are considerably different from those of the Miocene (17–14 Ma) mineralization.     

Constraints of Sr isotopic compositions of apatite and carbonates on the origin of Fe and Cu mineralizing fluids in the Lala Fe-Cu-(Mo,LREE) deposit,SW China

Numerous Fe-Cu deposits with mineralization styles similar to iron oxide-copper gold (IOCG) deposits form the Kangdian Fe-Cu metallogenic province, southwestern (SW) China. As one of the largest deposits in the region, the ~ 1.0 Ga Lala Fe-Cu deposit is hosted in a Paleoproterozoic volcanic-sedimentary succession named the Hekou Group which is alternately intruded by ~ 1.0 Ga doleritic plutons. This deposit has a paragenetic sequence evolving from Stage I of Na-alteration to Stage II of Fe mineralization, and finally to Stage III of Cu-(Mo, REE) mineralization, coeval with mafic-felsic intra-plate magmatism in the region. This study conducted in-situ Sr isotopic analyses on apatite and carbonate, aiming to resolve the long controversial issue regarding the origin of the Fe and Cu mineralizing fluids in the deposit. Apatite of Stage II has ⁸⁷Sr/⁸⁶Sr ratios varying from 0.71380 to 0.72733, much higher than those of synchronous igneous rocks in the region (0.7074 to 0.7091), but similar to the Paleoproterozoic host rocks (0.71368 to 0.71837 at ~ 1.0 Ga). This similarity indicates that radiogenic Sr of the Fe mineralizing fluid was dominantly sourced from the host rocks. Apatite and calcites of Stage III have ⁸⁷Sr/⁸⁶Sr ratios (0.75758–0.79293) much higher than apatite of Stage II and the host rocks but similar to the Archean basement rocks (as high as 0.80 at ~ 1.0 Ga) beneath the cover of the Yangtze Block, suggesting that the highly radiogenic Sr isotopic composition of the Cu mineralizing fluid was mainly inherited from the old basement rocks. In combination with previous C-O-S isotopic data indicating a magma-hydrothermal origin, it was suggested that the Fe mineralizing fluid was exsolved from a mafic magma that generated the ~ 1.0 Ga doleritic plutons, and inherited radiogenic Sr from the host rocks during fluid-rock interaction. By contrast, the Cu mineralizing fluid might have been sourced from another pulse of magmatic, Cu-Mo-REE- and CO₂-rich fluid which have once interacted with Archean basement rocks prior to mineralization. The source of such a Cu-Mo-REE-rich fluid was not well constrained in current study but was inferred to be exsolved from a hidden felsic magma. We propose that intrusions of the bimodal magmas in Kangdian are responsible for regional hydrothermal circulation which led to Fe-Cu-(Mo, REE) mineralization in the Kangdian province.     

Synmetamorphic Cu remobilization during the Pan-African orogeny: Microstructural,petrological and geochronological data on the kyanite-micaschists hosting the Cu(–U) Lumwana deposit in the Western Zambian Copperbelt of the Lufilian belt

The Pan-African Lufilian orogenic belt hosts world-class Cu deposits. In the Congolese Copperbelt (DRC), Cu(–Co) deposits, are mostly hosted within evaporitic and siliciclastic Neoproterozoic metasedimentary rocks (Mines Subgroup) and are interpreted as syn- to late-diagenetic deposits. In this paper, we present new data on Cu(–U) deposit hosted in metamorphic rocks of the internal zone of the Lufilian belt known as the Western Zambian Copperbelt in which a primary Cu mineralization is overprinted by a second syn-metamorphic Cu mineralizing event. This mineralizing event is synchronous with the Pan-African metamorphism affecting both the pre-Katanga basement and the Katanga metasedimentary sequence. Cu(–U) occurrences in the Western Zambian Copperbelt are hosted by kyanite-micaschists metamorphosed in the upper amphibolite facies.Mineral inclusions of graphite, micas and sulfides in kyanite porphyroblasts of the Cu-bearing kyanite-micaschists in the Lumwana Cu deposit point to a sedimentary protolith with relics of an inherited Cu stock. Based on petrologic, microstructural and geochronological evidence, we propose that this initial Cu-stock was remobilized during the Pan-African orogeny. Graphite, micas and sulfides preserved in a first generation of kyanite poikiloblasts (Ky₁) define an inherited S_0/1 foliation developed during the prograde part of the P–T path (D₁ deformation-metamorphic stage) reaching HP–MT metamorphic conditions.Remobilization during the retrograde part of the P–T path is evidenced by chalcopyrite–pyrrhotite and chalcopyrite–bornite delineating a steep-dipping S₂ schistosity and by chalcopyrite and bornite delineating a shallow-dipping S₃ schistosity associated with top to the south kinematic criteria. This retrograde path is coeval with ductile deformation in the kyanite field as evidenced by a second generation of synkinematic kyanite porphyroblasts (Ky₂) transposed in the S₃ schistosity (Ky_2–3), and is marked by progressive cooling from ca. 620 °C down to 580 °C (rutile geothermometry). Syn-S_2–3 metamorphic monazite grains yield U–Th–Pb ages ranging from ca. 540 to 500 Ma.Final retrogression and remobilization of Cu is marked by recrystallization of the sulfides in top to the north C₃ shear bands associated with rutile crystals yielding temperatures from ca. 610 to 540 °C. This final remobilization is younger than ca. 500 Ma (youngest U–Th–Pb age on syn-S₃ recrystallized monazite). These data are consistent with successive Cu remobilization for more than 40 Ma during Pan-African reworking of sediment-hosted deposits either from the basement of the Katanga sedimentary sequence or from the Katanga sequence itself marked by burial (D₁), syn-orogenic exhumation (D₂), and post-orogenic exhumation during gravitational collapse (D₃).     

西藏甲玛铜多金属矿床铜山矿体为manto型矿体?

manto型矿化是指"沿层交代"并受地层控制,构造控矿,品位高,富含硫化物矿石。甲玛铜多金属矿床位于西藏冈底斯成矿带东段,在公益性与商业性勘查结合下,取得重大找矿突破的世界级超大型斑岩-矽卡岩型铜多金属矿床。铜山(南坑)矿体是继揭露甲玛深部斑岩矿体之后的又一找矿重大突破。铜山矿体规模达到大型,铜金属量70多万吨,钼金属量2万吨,铅+锌金属量120多万吨,伴生金金属量20多吨,伴生银金属量2 000多吨。铜山矿体距离斑岩体中心1 km,受铜山滑覆构造控制,滑覆体内部次级褶皱、裂隙发育,为热液流体运移、沉淀提供了良好的空间;赋存于林布宗组角岩、林布宗组角岩和多底沟组大理岩层间及多底沟组大理岩中,呈透镜体、脉状、囊状、豆荚状;富含硫化物,主要为黄铜矿、闪锌矿、方铅矿、斑铜矿、磁黄铁矿、黄铁矿、辉钼矿等;品位较高,铜平均品位0.99%,铅+锌平均品位2.88%。通过野外地质调查,并与世界上其他manto型矿体对比,甲玛铜山矿体属于斑岩成矿系统远端的manto型富矿体。甲玛manto型矿体的发现和确定在西藏冈底斯成矿带上尚属首例,对该成矿带其他斑岩、矽卡岩矿床寻找外围manto型富矿体具有极其重要的指导意义,其经济意义也十分巨大,目前已经建成日处理4万吨的露天采场。     

Zircon U–Pb,Molybdenite Re–Os and K‐feldspar 40Ar/39Ar Dating of the Bolong Porphyry Cu–Au Deposit,Tibet, China

The Bolong porphyry Cu–Au deposit is a newly discovered deposit in the central Tibetan Plateau, and is ranked as the second largest copper deposit discovered to date in the Bangong‐Nujiang metallogenic belt in China. Three granodiorite porphyry phases occur within the Bolong porphyry Cu–Au deposit. Phyllic alteration is widespread on the surface of the deposit, and potassic alteration occurs at depth, associated with granodiorite porphyries. The copper and gold mineralization is clearly related to the potassic and phyllic alteration. Multiple chronometers were applied to constrain the timing of magmatic–hydrothermal activity at the Bolong deposit. Zircon U–Pb geochronology reveals that the granodiorite porphyry phases were emplaced at ca. 120 Ma. Re–Os data of four molybdenite samples from quartz–molybednite veinlets yielded an isochron age of 119.4 ± 1.3 Ma. The plateau age of hydrothermal K‐feldspar from the potassic alteration zone, analyzed by ⁴⁰Ar/³⁹Ar dating, is 118.3 ± 0.6 Ma, with a similar reverse isochron age of 118.5 ± 0.7 Ma. Therefore, the magmatic–hydrothermal activity occurred at ca. 120–118 Ma, which is similar in age to the neighboring Duobuza porphyry copper deposit. The period of 120–118 Ma is therefore important for the development of porphyry Cu–Au mineralization in the central Tibetan Plateau, and these porphyry deposits were formed during the final stages of the northward subduction of the Neo‐Tethys Ocean.     

Preliminary analysis on roles of metal–organic compounds in the formation of invisible gold

The paper comprises new analytical data on the nature and occurrence of gold in solid pyrobitumen, closely associated with the main gold-bearing sulfide arsenic ores of the Bakyrchik gold deposit (Kazakhstan), related to post-collisional magmatic-hydrothermal origin. Gold mineralization of the deposit occurs mainly in the form of an “invisible” type of gold in the structures of arsenian pyrite and arsenopyrite, and the form of gold-organic compounds of pyrobitumen in carbonaceous-terrigenous sequences of Carboniferous formation. Microscopic and electron microscopic analysis, Raman and FT-Infrared analysis, mineralogical and three-step sequential extraction analysis (NH₂OH·HCl, H₂O_2, HNO₃ + HCl) has been carried out using 9 ore samples (from 3 different types of ores) for a comprehensive study of pyrobitumen and sulfide arsenic ores focusing mainly on organic matter. The sequentially extracted precious metal content of pyrobitumen reaches up to 7 ppm gold and other metals like Ag 4 ppm, Pt 31 ppb, and Pd 26 ppb, forming metal–organic compounds, while arsenic sulfide minerals incorporate 11 ppm gold, 39 ppm Ag, 0.49 ppm Pt. The enrichment of gold associating with organic matter and sulfide ore minerals was confirmed in this study. Organic matter was active in the migration of gold and the capture of gold by pyrobitumen. Moreover, the reductive organic matter agent released gold, most likely for the sulfide arsenic ore minerals. Pyrobitumen was a decisive factor in the concentration, transportation, and preservation of gold in the deposit.

     

Mineralogy and Formation Conditions of Novoshirokinsky Base Metal–Gold Deposit,Eastern Transbaikal Region,Russia

This article presents the new mineralogical, fluid inclusion, and isotopic data for ores of the Novoshirokinsky base metal–gold deposit. Mineralogical sequence is supplemented and specified. The mineral assemblages containing native gold are studied. Morphology, grain size and chemical composition of native gold are described. Major parameters and composition of mineralizing fluids of the main ore stages at the deposit are estimated: main base metal (mid-temperature conditions, fluid salinity 3.1–13.1 wt % equiv NaCl) and carbonate–base metal (low-temperature conditions, fluid salinity 1.0–12.9 wt % equiv. NaCl). Sulfur isotopic composition of sulfides from commercial mineral assemblages has been studied. The δ³⁴S value (+10.5 ± 1‰) of mineralizing fluid has been calculated. The Novoshirokinsky deposit is similar to epithermal deposits and is spatially related to the Late Jurassic porphyry system. Evidence is provided on carbonate rocks of basement involved in the ore-forming process.     

Regional Metallogenesis of the Chang’an Gold Ore Deposit in Western Yunnan: Evidences from Fluid Inclusions and Stable Isotopes

<正>The Chang'an gold ore deposit in western Yunnan is located at the southern segment of the Ailaoshan metallogenic belt.The ore bodies are preserved in fractured Ordovician sedimentary clastic rocks.The gold-bearing minerals occur dominantly in sulfide-quartz veins.Fluid inclusion analysis shows that the Chang'an gold ore deposit is characterized by epithermal gold mineralization at temperatures between 200℃and 280℃at a shallow crustal level.The mineralizing fluids have intermediate to low salinity(6%-18%) and low densities(0.72-1.27 g/cm~3).The ore minerals haveδ~(34)S in a range from -13‰to 3.57‰,concentrated from -2.06‰to 3.57‰with an average of 1.55‰.The ~(206)Pb/~(204)Pb,~(207)Pb/~(204)Pb and ~(208)Pb/~(204)Pb values are 18.9977-19.5748,15.7093-15.784,39.3814-40.2004 respectively.These isotope data suggest that the ore-forming elements were mainly derived from mixed crustal and mantle sources.The Chang'an gold ore deposit and Tongchang Cu-Mo deposit are closely related to each other in their spatial distribution and age of formation.They have similar sources of mineralizing elements and identical ore-forming metal elements,and show a close relationship in physical and chemical conditions of mineralization.The two deposits constitute an epithermal-porphyry -skarn type Cu-Mo-Au mineralization system in the Tongchang-Chang'an area,which is related to the Cenozoic high-K alkaline magmatism.     

The Aitik Cu–Au–Ag deposit in northern Sweden: a product of high salinity fluids

The Aitik Cu–Au–Ag deposit is located in northern Sweden and is hosted by strongly deformed 1.9 Ga Svecofennian volcano-sedimentary rocks. The main copper mineralization, which occurs as disseminations and veinlets, is hosted by garnet–biotite schist. Subeconomic mineralization in the footwall to the ore is hosted by feldspar–biotite–amphibole gneiss and porphyritic quartz monzodiorite. The deposit has been affected by post-mineralization metamorphic and igneous activity. Fluid inclusions in six samples of copper-mineralized quartz veins record the presence of three different fluid populations. The main ore was deposited from an aqueous, highly saline (31–37 eq. wt% NaCl + CaCl₂) fluid. This fluid was trapped in inclusions intimately associated with the main chalcopyrite mineralization. Later bornite deposition took place from a less saline (18–27 eq. wt% NaCl + CaCl₂), aqueous fluid. A third fluid composed of almost pure CO₂, interacted with the copper-rich system during a post-ore event. The Aitik Cu–Au–Ag deposit shares some features with both porphyry-type and Fe-oxide–Cu–Au deposits. A high calcium content of the ore fluids, similar to other Cu–Au deposits in northern Scandinavia, suggests a contribution to the salinity of the mainly magmatic-hydrothermal fluids from evaporitic rocks in stratigraphically lower units.     

Chemical differences between minerals from mineralizing and barren intrusions from some North American porphyry copper deposits

Major-element analyses (by electron microprobe) and copper contents (by ion-probe) are reported for primary biotite, amphibole, magnetite, pyroxene, ilmenite, sphene and secondary biotite from intrusive rocks from mineralizing and barren stocks. The districts studied include Christmas, Globe-Miami, Sierrita and Tombstone, in Arizona; Bingham and Alta, Utah; Ely, Nevada; and Brenda, British Columbia. Amphiboles from barren rocks are relatively iron-rich and display only minor compositional variation. In contrast, amphiboles from mineralizing rocks span the range from magnesio-hornblende to actinolite, commonly even within one grain. Barren intrusions (type B) that are temporally distinct from mineralizing intrusions, and barren intrusions outside areas of known mineralization have higher Cu contents in their constituent minerals than do mineralizing intrusions. Barren intrusions (type A) that are deep-level temporal equivalents of Cu-bearing porphyritic rocks are depleted in copper. This suggests that copper is abstracted from not only the apical portions of porphyries but from parts of the deeper parent intrusions. The Cu contents of biotites (av. 23 ppm) and magnetites (97 ppm) from barren type B intrusions contrast with those from mineralizing intrusions, with biotites containing 7 ppm Cu and magnetites 3 ppm Cu. Primary amphiboles from all intrusive rock types have low copper contents, typically 2 to 5 ppm. In the continental North American deposits, the amount of copper available by liberation from or non-incorporation into amphibole, biotite and magnetite during magmatic crystallization or the early hydrothermal stage is low, perhaps too low to be the sole source of copper mineralization, unless copper is abstracted from large volumes (∼ 100 km³) of rock. These results contrast with a study of the island-arc porphyry copper at Koloula, Guadalcanal, where it was argued that sufficient copper for mineralization could have been abstracted from relatively small volumes of host rocks that originally contained as much Cu as the contemporaneous barren rock types.     

The geology and geochemistry of the Lumwana Cu (± Co ± U) deposits, NW Zambia

The Lumwana Cu (± Co ± U) deposits of NW Zambia are large, tabular, disseminated ore bodies, hosted within the Mwombezhi Dome of the Lufilian Arc. The host rocks to the Lumwana deposits are two mineralogically similar but texturally distinct gneisses, a granitic to pegmatitic gneiss and a banded to augen gneiss which both comprise quartz–feldspar ± biotite ± muscovite ± haematite ± amphibole and intervening quartz–feldspar ± biotite schist. The sulphide ore horizons are typically developed within a biotite–muscovite–quartz–kyanite schist, although mineralization locally occurs within internal gneiss units. Contacts between the ore and host rocks are transitional and characterized by a loss of feldspar. Kinematic indicators, such as S-C fabrics and pressure shadows on porphyroblasts, suggest a top to the north shear sense. The sulphides are deformed by a strong shear fabric, enclosed within kyanite or concentrated into low strain zones and pressure shadows around kyanite porphyroblasts. This suggests that the copper mineralization was introduced either syn- or pre-peak metamorphism. In addition to Cu and Co, the ores are also characterized by enrichments in U, V, Ni, Ba and S and small, discrete zones of uranium mineralization, occur adjacent to the hanging wall and footwall of the copper ore bodies or in the immediate footwall to the copper mineralization. Unlike typical Copperbelt mineralization, unmineralized units show very low background copper values. Whole rock geochemical analyses of the interlayered schist and ore schist, compared to the gneiss, show depletions in Ca, Na and Sr and enrichments in Mg and K, consistent with replacement of feldspar by biotite. The mineral chemistry of muscovite, biotite and chlorite reflect changes in the bulk rock chemistry and show consistent increases in X _Mg as the schists develop. δ³⁴S for copper sulphides range from +2.3?‰ to +18.5?‰, with pyrite typically restricted to values between +3.9?‰ and +6.2?‰. These values are atypical of sulphides precipitated by bacteriogenic sulphate reduction. δ³⁴S data for Chimiwungo (Cu + Co) show a broader range and increased δ³⁴S values compared to the Malundwe (Cu) mineralization. The Lumwana deposits show many characteristics which distinguish them from classical Copperbelt mineralization and which suggests that they are formed by metasomatic alteration, mineralization and shearing of pre-Katangan basement. Although this style of mineralization is reported elsewhere in the Copperbelt, sometimes associated with the more widely reported stratiform ores of the Lower Roan, none of the previously reported occurrences have so far developed the tonnages of ore reported at Lumwana.