Stratabound Copper Deposits Research Articles

Neotocite textures as a clue to the exploration of Red Bed type sediment-hosted stratabound copper (SSC) deposits – evidence from Ravar–Tabas–Eshghabad copper belt, Central Iran

ABSTRACT Red Bed type sediment-hosted stratabound copper (SSC) deposits consist of replaced, disseminated to veinlets copper sulphides, hosted by thick, haematite-stained sequences of sandstone, conglomerate, and siltstone. More than 120 sediment-hosted stratabound copper (SSC) deposits and occurrences have been reported in Iran. Ravar–Tabas–Eshghabad is the major Red Bed type SSC belt in Iran, with a cumulative tonnage of more than 400 Mt ore at ~1–2% Cu. These deposits are hosted in Garedu Red Bed Formation (including reddish conglomerates and micro-conglomerates, red siltstones and sandstones), and copper sulphides (chalcocite, with minor chalcopyrite and bornite) are concentrated in local reducing conditions that are achieved around plant fossil accumulations, within grey paleochannels in the upper part of the Garedu Red Bed Formation. These deposits are usually explored using geochemical, geophysical, and remote sensing methods. However, the host layers usually extend laterally up to tens of kilometres, and the critical point is to find the paleochannels in the host horizons where organic matter and plant fossils accumulate, especially in underground mining and boreholes. The lateral extension of ore-bearing lenses is usually 50–150 m, so it is not easy to find them within the reduced horizons. Recognizing neotocite textures (including diffusion, radial DLA (diffusion-limited aggregation), cat footprint, and spotty), and distribution in the host rocks of the Red Bed type SSC deposits can be used as a clue to find the ore lenses, organic matter, and plant fossil accumulations.

Neoproterozoic Zn-Pb mineralization in the world-class Sichuan-Yunnan-Guizhou Zn-Pb triangle, southwest China: Insights from apatite geochemistry and in situ sericite Rb-Sr geochronology of the Daxiao deposit

The Sichuan-Yunnan-Guizhou (SYG) zinc-lead triangle, located in southwestern China, is an important producer of zinc, lead, silver, and critical raw metals such as germanium. In this region, most Zn-Pb deposits hosted in the later Ediacaran to Permian carbonate rocks are believed to be Mississippi Valley-type (MVT) deposits, while the origin of the Zn-Pb deposits found in the Mesoproterozoic basement remains controversial. To address this gap, our study conducted in situ LA-ICP-MS/MS muscovite Rb-Sr dating and apatite major, trace and Sr isotope analysis on the Daxiao deposit hosted in the Mesoproterozoic basement. The in situ Rb-Sr dating of sericite yielded a Neoproterozoic age of 766 ± 31.3 Ma, challenging the previously proposed Indosinian orogen-related MVT model. Instead, it links the formation of this deposit to an extensional setting that coincided with the breakup of the Rodinia. We identified a specific type of apatite, recognized as ore-stage apatite based on texture and analyzed composition, within the deposit. The ore-stage apatite exhibits high 87Sr/86Sr ratios (ranging from 0.78384 to 0.81082), similar to those of the Archean basement rocks.Based on our study and previous data, we proposed a new genetic model for the Daxiao Zn-Pb deposit, and possibly other basement-hosted Zn-Pb deposits in the SYG triangle. During the Neoproterozoic (∼766 Ma), the study area experienced an extensional setting characterized by crustal thinning and magmatic activity resulting from the breakup of the Rodinia. Basinal brines infiltrated the deep Archean basement along faults and were heated to high temperatures by magma and/or high geothermal gradients. These hot brines continuously extracted Pb, Zn from the Archean basement and migrated upward into the Mesoproterozoic host rock, where they precipitated lead–zinc ores in favorable structural positions. The Daxiao Zn-Pb deposit, along with the coexisting sediment-hosted stratabound copper (SSC) deposits, basement-hosted gold and uranium deposits, and late sulfide mineralization in the iron oxide-copper–gold (IOCG) deposits, suggests a Neoproterozoic regional mineralization event associated with the breakup of Rodinia. Our study also highlights the potential of using in situ sericite Rb-Sr dating to precisely determine the age of other hydrothermal ore deposits, such as Carlin-type Au deposits, which have long been a subject of uncertainty.

Reconstruction of Copper Smelting Technology Based on 18–20th-Century Slag Remains from the Old Copper Basin, Poland

This research was conducted on historical copper slags from Leszczyna and Kondratów in Lower Silesia, Poland. The area, formerly known as the Old Copper Basin, was a mining and smelting centre between the 18th and 20th centuries, with a dominant period in the 19th century. Cu-carbonates and residual chalcocite dominate local strata-bound copper deposits. Ore bodies are restricted to carbonate strata. A geochemical and mineralogical study of slag samples from four research sites allowed us to establish that a low amount of sulphur in slags results from S-poor ores, and pyrite with gypsum was implemented as reducing agents. Arkose sandstones served as a flux. During smelting, oxygen availability was limited, and temperature exceeded 1200 °C (18th- and 19th-century smelting) and 1400 °C (20th-century smelting). Calculated viscosity indexes mark the low efficiency of metal separation between the silicate and metallic phases. The skeletal and dendritic form of the crystals proved that slag melt was relatively rapidly cooled after formation, usually in air conditions. We estimated that approx. 2000 m3 of slag was created during the leading smelter (Stilles Glück) activity. The research provided various details of the historical copper smelting technological process in Leszczyna and Kondratów.

Mesoproterozoic porphyry copper mineralization at Mamainse Point, Ontario, Canada in the context of Midcontinent rift metallogeny

The Jogran copper prospect in southern Ontario, Canada, is located on the northeastern shoulder of the North American Midcontinent rift system where it is centered on two small, closely spaced quartz monzonite porphyry intrusions emplaced into Neoarchean mafic metavolcanic rocks. Notwithstanding an atypical alteration zoning pattern, the distinctive alteration styles and veinlet types confirm its porphyry copper affiliation. Two samples of molybdenite from chalcopyrite-bearing quartz veinlets in the two centers returned Re-Os ages of 1101 ± 5 and 1094 ± 5 Ma, showing that the mineralization took place during the main stage of extension and magmatic activity that gave rise to the Midcontinent rift and associated large igneous province (LIP). The nearby copper-bearing Tribag breccia pipes and Coppercorp veins have been shown previously to also be intrusion related, and likely formed penecontemporaneously with Jogran. The Jogran and nearby copper mineralization overlapped temporally with generation of low-grade magmatic copper-nickel-PGE deposits in the Duluth intrusive complex but predated the strata-bound native copper and chalcocite deposits in the Keweenaw Peninsula, which are believed to have formed from basinal fluids during rift inversion. Although such magmatic and strata-bound copper deposits typify intracontinental rift metallogeny, porphyry copper deposits are normally confined to convergent margin magmatic arcs, thereby making the rift-LIP setting of Jogran exceptional and possibly unique.

مطالعات کانی سازی، ژئوشیمی، سیالات درگیر و ایزوتوپ پایدار گوگرد کانسار Cu-Zn-As باقرق با سنگ میزبان کربناته (شمال شرق انارک)

کانسار Cu-Zn-As باقرق در شمال شرق شهر انارک و در استان اصفهان قرار دارد. کانی‌سازی به‌صورت دیرزاد، ماهیت چینه‌کران و بافت و ساخت پرکننده فضای خالی در سنگ میزبان کربناتی رخداده است. کانی‌شناسی بخش درون‌زاد شامل کالکوسیت، کالکوپیریت، پیریت، اسفالریت، گالن، انارژیت، باریت و کلسیت و کانیهای بخش برون‌زاد شامل مالاکیت، آزوریت، کوولیت، کریزوکولا، کالکوسیت، سروزیت، اسمیت‌زونیت، مس طبیعی، هماتیت، گوتیت و لیمونیت می‌باشد. سنگ میزبان کربناتی در اطراف زون‌های کانه‌دار متحمل دگرسانیهای دولومیتی‌شدن و کلسیتی‌شدن شده است. مس به‌عنوان عنصر اصلی ذخیره (با میانگین 28/20 درصد وزنی) و پس از آن عناصر روی (با میانگین تقریبی 1 درصد وزنی) و آرسنیک (با میانگین تقریبی 1 درصد وزنی) می‌باشند. مطالعات سیالات‌درگیر روی کانی باریت نشان می‌دهد سیال کانه‌دار سولفیدی دارای محدوده دمای همگن شدن بین 259 تا 354 درجه سانتی‌گراد و میزان شوری بین 8 تا 13 درصد وزنی معادل NaCl می‌باشد. سیال کانه‌دار در مراحل پایانی کانی‌سازی با آبهای جوی دچار اختلاط شده و فاز تأخیری غیر سولفیدی کلسیتی با محدوده دمای نسبتا پایین ‌(78 تا 112 درجه سانتی‌گراد) و درجه شوری پایین (بین 3 تا 6 درصد وزنی معادل NaCl) را تشکیل داده است. محدوده مقادیر 34Sδ کانی‌ باریت کانسار باقرق بین 13+ تا 14+ در هزار بوده در حالی‌که محاسبه مقدار 34Sδ مربوط به سیال کانه‌دار پس از تصحیح دمایی بین 7- تا 8- در هزار به‌دست آمد. منشأ گوگرد باقرق با توجه به شباهت ایزوتوپ باریت با سولفات‌های دریایی کرتاسه، احتمالا از لایه‌های تبخیری این دوره زمانی تأمین شده است. این سولفا‌ت‌ها توسط فرآیند‌های ترموشیمیایی به‌صورت بخشی به گوگرد احیایی با مقدار ایزوتوپی سبک‌تر (حدود 21 در هزار) تبدیل و جهت ته‌نشست سولفیدها مورد استفاده قرار گرفته است. کانسار باقرق با توجه به خصوصیاتی همچون سنگ میزبان کربناته، غیاب فعالیت آذرین، بافت پرکننده فضای خالی، دگرسانی دولومیتی،کانی‌شناسی، ژئوشیمی ماده‌معدنی (وجود As و Sb بالا و عدم حضور Bi)، داده‌های دماسنجی و مقادیر ایزوتوپ گوگرد، شباهت زیادی با کانسارهای مس با سنگ میزبان کربناته در افریقا و به‌ویژه نوع سومب (Tsumeb) در نامیبیا نشان می‌دهد. کانسار باقرق احتمالا مرتبط با سیالات دگرگونی آزاد شده در حین فازهای کوه‌زایی مرتبط با بسته‌شدن اقیانوس نئوتتیس می‌باشد.

Geologic, Fluid Inclusion and Stable Isotope Constraints on Mechanisms of Ore Deposition at the Datuanshan Copper Deposit, Middle–Lower Yangtze Valley, Eastern China

The Datuanshan deposit is one of the largest and most representative stratabound copper deposits in the Tongling area, the largest ore district in the Middle–Lower Yangtze River metallogenic belt. The location of the orebodies is controlled by the interlayer–slipping faults between the Triassic and Permian strata, and all the orebodies are distributed in stratiform shape around the Mesozoic quartz monzodiorite dikes. Based on field evidence and petrographic observations, four mineralization stages in the Datuanshan deposit have been identified: the skarn, early quartz–sulfide, late quartz–sulfide and carbonate stages. Chalcopytite is the main copper mineral and mainly formed at the late quartz–sulfide stage. Fluid inclusions at different stages were studied for petrography, microthermometry, laser Raman spectrometry and stable isotopes. Four types of fluid inclusions, including three‐phase fluid inclusions (type 1), liquid‐rich fluid inclusions (type 2), vapour–rich fluid inclusions (type 3) and pure vapour fluid inclusions (type 4), were observed. The minerals from the skarn, early and late quartz–sulfide stages contain all fluid inclusion types, but only type 2 fluid inclusions were observed at the carbonate stage. Petrographic observations suggest that most of the inclusions studied in this paper are likely primary. The coexistence of different types of fluid inclusions with contrasting homogenization characteristics (to the liquid and vapour phase, respectively) and similar homogenization temperatures (the modes are 440–480°C, 380–400°C and 280–320°C for the skarn, early and late quartz–sulfide stages, respectively) in the first three stages, strongly suggests that three episodes of fluid boiling occurred during these stages, which is supported by the hydrogen isotope data. Laser Raman spectra identified CH4 at the skarn and early quartz–sulfide stages. Combined with other geological features, the early ore–forming fluids were inferred to be under a relatively reduced environment. The CO2 component has been identified at the late quartz–sulfide and carbonate stages, indicating that the late ore‐forming fluids were under a relatively oxidized environment, probably as a result of inflow of and mixing with meteoric water. In addition, microthermometric results of fluid inclusions and H–O isotope data indicate that the ore forming fluids were dominated by magmatic water in the early stages (skarn and early quartz–sulfide stages) and mixed with meteoric water in the late stages (late quartz–sulfide and carbonate stages). The evidence listed above suggests that the chalcopyrite deposition in the Datuanshan deposit probably resulted from the combination of multi‐episode fluid boiling and mixing of magmatic and meteoric water.

Joint Simulation of Grade and Rock Type in a Stratabound Copper Deposit

This work deals with the joint simulation of copper grade (as a continuous regionalized variable) and rock type (as a categorical variable) in Lince–Estefania deposit, located in northern Chile. The region under study is heterogeneous, containing three main rock types (intrusive, andesite and breccia bodies) with different copper grade distributions. To perform joint simulation, the multi-Gaussian and pluriGaussian models are used in a combined form. To this end, three auxiliary Gaussian random fields are considered, one for simulating copper grade, up to a monotonic transformation, and two for simulating rock types according to a given truncation rule. Furthermore, the dependence between copper grade and rock types is reproduced by considering cross correlations between these Gaussian random fields. To investigate the benefits of the joint simulation algorithm, copper grade and rock types are also simulated by the traditional cascade approach and the results are compared. It is shown that the cascade approach produces hard boundaries, that is, abrupt transitions of copper grades when crossing rock-type boundaries, a condition that does not exist in the study area according to the contact analysis held on the available data. In contrast, the joint simulation approach produces gradual transitions of the copper grade near the rock-type boundaries and is more suited to the actual data.

Discovery of strata-bound copper deposit in the Arqueros area, Northern Chile

Discovery of strata-bound copper deposit in the Arqueros area, Northern Chile

Late Paleoproterozoic to Early Mesoproterozoic Tangdan Sedimentary Rock-Hosted Strata-bound Copper Deposit, Yunnan Province, Southwest China

Sedimentary rock-hosted strata-bound copper deposits are widespread in the Kangdian region of the Central Yunnan and southern Sichuan provinces, southwest China. The deposits occur within weakly metamorphosed rocks of the late Paleoproterozoic to early Mesoproterozoic Dongchuan Group and are spatially associated with discordant breccia bodies that are interpreted as having formed from salt diapirs. The Tangdan deposit, the largest in the region, consists of stratiform and discordant orebodies predominantly hosted in dolostones immediately above hematitic sandstones and siltstones and in black shales above the dolostones. Host rocks for the deposit display a complex paragenetic sequence of alteration and mineralization. Early sodic alteration resulted in the growth of both albite and ferroan dolomite. Later potassic alteration resulted in the precipitation of potassium feldspar and locally biotite in argillaceous layers. Sulfide mineralization was temporally and spatially associated with silicification that postdated both sodic and potassic alteration. Textures suggest that silicification may have preferentially affected evaporite minerals in the dolostones. Copper sulfides form bedding-parallel disseminations, veinlets and, to a lesser extent, stockworks. Copper sulfides are dominated by chalcopyrite with lesser bornite and chalcocite. Hypogene chalcopyrite and bornite from the Tangdan deposit have δ34S values that range from −12.7 to +9.3‰ and cluster between −3 to +5‰. The values suggest derivation from Mesoproterozoic marine sulfates. The dolostone host rocks have relatively homogeneous C and O isotope values ranging from 0.2 to 1.3‰ δ13CV-PDB and from 19.1 to 22.4‰ δ18OV-SNOW. Carbonate minerals in quartz sulfide veins display both a trend toward lighter oxygen isotope values and a trend to significantly lighter carbon isotope values. The light carbon isotope values suggest involvement of organic carbon in the mineralizing process. Alteration and mineralization at Tangdan probably occurred via interaction of oxidized saline brines derived from the underlying red-bed sequence with partially to wholly lithified dolostones. Sulfide precipitation was likely due to both redox reactions and mineralizing fluid pH changes resulting from dolomite and sulfate dissolution. The styles of alteration and mineralization at the Tangdan deposit are similar to those observed in the Central African Copperbelt, particularly the dolostone-hosted orebodies in the Mines Series of the Democratic Republic of Congo.

A Study on the Kunyang Aulacogen

The Kunyang Aulacogen is a continental rift which initiated at the beginning of the Middle Proterozoic. It was generated on the rigid continental crust represented by the crystalline Kangding Complex, and is bounded by two N-S-trending deep faults?Anninghe-Luzhijiang Fault and Xiaojiang Fault. Its early stage of rupture was characterized by alkaline mafic igneous activities in the Dahongshan Group and Hekou Group. During the later tensile- depression stage the aulacogen evolved into a graben where sedimentation of the Kunyang Group took place. The sedimentary sequence comprises terrestrial red beds, algal dolomite, marine black shale and carbonate rocks which are quite typical of rift sedimentary association, and contains stratabound copper deposits of the well-known Dongchuan type.

Genesis and Evolution of Bitumen in Lower Cretaceous Lavas and Implications for Strata-bound Copper Deposits, North Chile

Small, strata-bound copper sulfide deposits are found associated with bitumen in Lower Cretaceous basaltic andesite flows of the Pabellon Formation near Copiapo, north Chile. The physical characteristics of the bitumen and hydrocarbon biomarkers provide clues to the genesis, evolution, and possible role during copper mineralization. Biomarker analysis reveals a predominantly bacterial origin, with minor contributions from phytoplankton and higher plants, which were deposited in a shallow marine environment. An expulsion temperature between 64° and 87°C was determined, typical for low maturity petroleum. This petroleum was altered during migration by mixing with brines, increasing its viscosity by aromatization and sulfurization. At the moment of the accumulation, the temperature of the brine was under 150°C. The viscous oil filled the primary and secondary porosity of the basaltic andesite, which acted as an oil trap. After the oil accumulation, a hotter, hydrothermal influx resulted in thermal alteration of the petroleum and a further decrease of light alkane concentrations. High sulfur concentrations in the hydrothermal fluids led to further aromatization of the organic compounds, generating highly alkylated benzonaptho- and dinaphthothiophenes. Copper in the sulfur-rich solutions was reduced, triggering the precipitation of bornite, chalcopyrite, digenite, chalcocite, and covellite through thermochemical sulfate reduction. The bitumen interacted with metals by virtue of its inherent reducing characteristics (activated carbon) and was itself oxidized to form a pyrobitumen residue.

Hydrothermal alteration and magnetic properties of rocks in the Carolina de Michilla stratabound copper district, northern Chile

In the Carolina de Michilla district, northern Chile, stratabound copper mineralization is hosted by Jurassic volcanic rocks along the trace of the Atacama fault system. In this study, we present the overall effects of hydrothermal alteration on the magnetic properties of rocks in this district. Two types of metasomatic alteration associations occur, one of regional extent and the other of local hydrothermal alteration associated with copper mineralization (e.g., Lince–Estefania–Susana). Regional alteration is interpreted as a low-grade “propylitic association” characterized by an epidote–chlorite–smectite–titanite–albite–quartz–calcite association. The local hydrothermal alteration is characterized broadly by a quartz–albite–epidote–chlorite–calcite mineral assemblage. The most pervasive alteration mineral is albite, followed by epidote and, locally, actinolite. These minerals contrast sharply against host rock minerals such as chlorite, calcite, zeolite, prehnite, and pumpellyite, but alteration is constrained to mineralized bodies as narrow and low contrast alteration halos that go outwards from actinolite–albite to epidote–albite, to epidote–chlorite, and finally to chlorite. Hydrothermal alteration minerals, compared to regional alteration minerals, show iron-rich epidotes, a lower chlorite content of the chlorite–smectite series, and a nearly total albite replacement of plagioclase in the mineralized zones. Opaque minerals associated with regional alteration are magnetite and maghemite, and those associated to hydrothermal alteration are magnetite, hematite, and copper sulphides. We present paleomagnetic results from nine sites in the Michilla district and from drill cores from two mines. Local effects of hydrothermal alteration on the original magnetic mineralogy indicate similar characteristics and mineralogy, except for an increase of hematite that is spatially associated with the Cu–sulphide breccias with low magnetic susceptibilities. Results indicate that it is impossible to magnetically differentiate mineralized bodies from unmineralized lavas, except for pyrite-rich hydrothermal breccias. In conclusion, for stratabound copper deposits of the Michilla type, the overall effect of hydrothermal alteration on the paleomagnetic properties of rocks is of low contrast, not clearly discernable even at a small scale. From an exploration point of view, magnetic exploration surveys should not discern mineralized bodies of Cu–sulphide breccias except in detailed ground surveys due to the small size of contrasting bodies. Unoriented drill cores with primary ore mineralization record a characteristic remanent magnetization of reverse polarity. Taking into account the azimuth and dip of the drill cores, we were able to compare the magnetization of the mineralized bodies with the characteristic directions from sites drilled in situ from Late Jurassic–Early Cretaceous intrusives mostly. The characteristic direction recorded by the Pluton Viera is similar to the magnetization of the ore bodies of the Estefania mine. If copper mineralization mostly postdates the tilt of the volcanic flows, the low paleomagnetic inclinations suggest an age for the mineralization near 145 Ma, the time of the lowest paleolatitude for the South American plate during the Mesozoic.

Nature, diversity of deposit types and metallogenic relations of South China

The South China Region is rich in mineral resources and has a wide diversity of deposit types. The region has undergone multiple tectonic and magmatic events and related metallogenic processes throughout the earth history. These tectonic and metallogenic processes were responsible for the formation of the diverse styles of base and precious metal deposits in South China making it one of the resource-rich regions in the world. During the Proterozoic, the South China Craton was characterised by rifting of continental margin before eruption of submarine volcanics and development of platform carbonate rocks, and the formation of VHMS, stratabound copper and MVT deposits. The Phanerozoic metallogeny of South China was related to opening and closing of the Tethyan Ocean involving multiple orogenies by subduction, back-arc rifting, arc–continent collision and post-collisional extension during the Indosinian (Triassic), Yanshanian (Jurassic to Cretaceous) and Himalayan (Tertiary) Orogenies. The Late Palaeozoic was a productive metallogenic period for South China resulting from break-up and rifting of Gondwana. Significant stratabound base and precious metal deposits were formed during the Devonian and Carboniferous (e.g., Fankou and Dabaoshan deposits). These Late Palaeozoic SEDEX-style deposits have been often overprinted by skarn systems associated with Yanshanian magmatism (e.g., Chengmenshan, Dongguashan and Qixiashan). A number of Late Palaeozoic to Early Mesozoic VHMS deposits also developed in the Sanjiang fold belt in the western part of South China (e.g., Laochang and Gacun). South China has significant sedimentary rock-hosted Carlin-like deposits, which occur in the Devonian- to Triassic-aged accretionary wedge or rift basins at the margin of the South China Craton. They are present in a region at the junction of Yunnan, Guizhou, and Guangxi Provinces called the ‘Southern Golden Triangle’, and are also present in NW Sichuan, Gansu and Shaanxi, in an area known as the ‘Northern Golden Triangle’ of China. These deposits are mostly epigenetic hydrothermal micron-disseminated gold deposits with associated As, Hg, Sb + Tl mineralisation similar to Carlin-type deposits in USA. The important deposits in the Southern Golden Triangle are Jinfeng (Lannigou), Zimudang, Getang, Yata and Banqi in Guizhou Province, and the Jinya and Gaolong deposits in Guangxi District. The most important deposits in the Northern Golden Triangle are the Dongbeizhai and Qiaoqiaoshang deposits. Many porphyry-related polymetallic copper–lead–zinc and gold skarn deposits occur in South China. These deposits are related to Indosinian (Triassic) and Yanshanian (Jurassic to Cretaceous) magmatism associated with collision of the South China and North China Cratons and westward subduction of the Palaeo-Pacific Plate. Most of these deposits are distributed along the Lower to Middle Yangtze River metallogenic belt. The most significant deposits are Tonglushan, Jilongshan, Fengshandong, Shitouzui and Jiguanzui. Au–(Ag–Mo)-rich porphyry-related Cu–Fe skarn deposits are also present (Chengmenshan and Wushan in Jiangxi Province and Xinqiao, Mashan-Tianmashan, Shizishan and Huangshilaoshan in Anhui Province). The South China fold belt extending from Fujian to Zhejiang Provinces is characterised by well-developed Yanshanian intrusive to subvolcanic rocks associated with porphyry to epithermal type mineralisation and mesothermal vein deposits. The largest porphyry copper deposit in China, Dexing, occurs in Jiangxi Province and is hosted by Yanshanian granodiorite. The high-sulphidation epithermal system occurs at the Zijinshan district in Fujian Province and epithermal to mesothermal vein-type deposits are also found in the Zhejiang Province (e.g., Zhilingtou). Part of Shandong Province is located at the northern margin of the South China Craton and the province has unique world class granite-hosted orogenic gold deposits. Occurrences of Pt–Pd–Ni–Cu–Co are found in Permian-aged Emeishan continental flood basalt (ECFB) in South China (Jinbaoshan and Baimazhai in Yunnan Province and Yangliuping in Sichuan Province). South China also has major vein-type tungsten–tin–bismuth–beryllium–sulphide and REE deposits associated with Yanshanian magmatism (e.g., Shizhuyuan and Xihuashan), important world class stratabound base metal–tin deposits (Dachang deposit), and the large antimony deposits (Xikuangshan and Woxi). During the Himalayan Orogeny, many giant deposits were formed in South China including the recently emerging Yulong and Gangdese porphyry copper belts in Tibet and the Ailaoshan orogenic gold deposits in Yunnan.

The role of bitumen in strata-bound copper deposit formation in the Copiapo area, Northern Chile

In northern Chile, between 27 and 33°S, there are numerous deposits where residual petroleum is associated with Cu-(Ag) mineralisation (the most famous being El Soldado). All of these deposits are hosted by Lower Cretaceous volcanic or volcanoclastic facies along the axis of a former backarc basin. This close relationship suggests that the generation, migration and emplacement of hydrocarbons in the Cretaceous volcanic units is a regional process, associated with the evolution of the Cretaceous backarc basin and points to the importance of pyrobitumen as an exploration tool for similar Cu–(Ag) deposits. The present work analyses four small strata-bound copper deposits located along a north–south belt approximately 10 km east of Copiapo in northern Chile. These deposits are typically hosted by pyrobitumen-rich andesitic volcanic to volcanoclastic rocks intercalated with the marine carbonate Pabellon Formation, the youngest formation within the Chanarcillo Group. The strong genetic and spatial relationships between the pyrobitumen-rich lavas and the mineral deposits allow us to define this volcanic belt as the Ocoita-Pabellon Metallotect. Two hydrothermal events can be distinguished based on the mineralogical, textural, fluid inclusion and isotope data of ore and gangue and on the optical properties of residual petroleum. During the early event, petroleum was mobilised from the source rocks into the primary and secondary porosity of the lavas by Fe-rich hydrothermal fluids, which precipitated pyrite as an early sulphide phase. The second event is characterised by Cu-rich hydrothermal fluids, which induced three successive sub-stages of Cu-sulphide precipitation. The hydrothermal fluids chemically and thermally altered the first-stage bitumen, transforming it into pyrobitumen. The present work documents similarities between the Ocoita-Pabellon Metallotect and the El Soldado ore deposit and emphasises important differences. In the El Soldado host rocks, a petroleum reservoir existed prior to the arrival of the mineralising hydrothermal fluids, the framboidal pyrite was formed by assistance of bacteria, the S of the Cu sulphides was inherited from the pyrite, and the fluid source was basin connate-metamorphic brine. In the Ocoita-Pabellon Metallotect, the hydrocarbons were mobilised into the host rocks by hydrothermal fluids; the pyrite is epigenetic, the δ34S values of pyrite and copper sulphides are very different, with distinctive light δ34S signature of Cu sulphides (δ34S between −44.7 and −17.9‰), and the calculated δ18O of hydrothermal fluids indicates the participation of meteoric water in the late phases of the hydrothermal system.

Re–Os isotope systematics for the Lince–Estefanía deposit: constraints on the timing and source of copper mineralization in a stratabound copper deposit, Coastal Cordillera of Northern Chile

The Lince–Estefania stratabound copper deposit in the Michilla district is one of the most important deposits in the Coastal Cordillera of northern Chile and is one of the most representative of this type of deposit. Chalcocite and bornite characterize the main stage of hypogene copper sulfide mineralization. Rhenium and osmium isotopes are used here to constrain the age of hypogene mineralization and the source of osmium contained in these ore minerals. A Re–Os isochron yielded an age of 160±16 Ma (2σ), with an associated initial 187Os/188Os ratio of 1.06±0.09 (mean square of weighted deviates=1.8). This age is consistent with available geochronological data from volcanic rocks that host the mineralization and associated alteration phases. The high initial 187Os/188Os ratio indicates a lower crustal component for the source of Os and, by inference, the Cu sulfides that contain this Os. Late hematite occurs as an isolated phase or, more commonly, is associated with the chalcocite–bornite and supergene chalcocite–covellite associations. Analyses performed on pure hematite indicate a disturbance of the Re–Os system, and hence, this mineral phase is not useful as a Re–Os geochronometer.

Hydrocarbon Involvement in the Genesis of Ore Deposits: An Example in Cretaceous Stratabound (Manto-Type) Copper Deposits of Central Chile

The analysis of the empirical association of organic carbon in its various forms (e.g., oil, gas, coal) with a variety of ore-deposit types can be a rewarding exercise in the formulation of genetic models and exploration. In many ore provinces, organic matter, residing in its source rocks, migrating in the form of hydrocarbons, or in transient, permanent, leaking, or degrading reservoirs, is likely to have interacted with ground waters, with hydrothermal solutions of diverse origin, or with magmas. After a brief review of these associations, we describe the ubiquitous occurrence of remnant petroleum in two representative “manto-type” stratabound copper deposits in Chile and suggest its possible genetic role and exploration significance. Overmature petroleum (solid bitumen, pyrobitumen) is found in association with copper ores in the southern orebodies of the El Soldado copper deposit in central Chile. Textures indicate that petroleum occupied the host-rock porosity before copper mineralization. Isotopic data for C and O in total organic carbon and carbonate confirm the affiliation with organic carbon and suggest that gangue carbonates are in part the result of the oxidation of hydrocarbons. Reflectance of the solid bitumen is highest near ore (BR o ∼ 4%), and its geochemistry (Rock-Eval) indicates that the residual hydrogen (i.e., hydrocarbon) content is very low. It is proposed that mineralizing solutions interacted with a pre-existing degraded hydrocarbon reservoir. The hydrocarbons physically prevented low-grade metamorphic minerals from sealing the porosity, were oxidized to form carbonate gangue and alteration, and possibly acted as a reductant at the site of sulfide precipitation. Copper sulfides (bornite, chalcocite, chalcopyrite) filled spaces among bitumen, carbonate, and pre-existing sulfides (arsenopyrite, pyrite) only after significant burial and faulting of the host volcanic strata and trachytic subvolcanic intrusives had occurred, after migration of liquid petroleum into the porosity and during or after its solidification there; this makes syngenetic and early diagenetic models previously proposed for the deposit untenable. Similar occurrences of bitumen in the ores of the Talcuna copper/manganese district and in several other stratabound copper deposits in central and north-central Chile suggest that organic matter may have been involved in the genesis of many Andean manto-type deposits. The identification of source-trap systems that could have generated oil or gas reservoirs, which in turn could have interacted later with hydrothermal solutions from various sources, may be a useful exploration model for metallic ore deposits in the back-arc basins of the Andes.

Metallogeny and lead isotopic composition of base metal sulfide deposits in the Rappen area, northern Sweden

Early Proterozoic volcanic and sedimentary rocks of the Rappen district in northern Sweden were deposited at a destructive plate margin to the south of the Archaean craton of the western Baltic Shield. The volcano-sedimentary suite was intruded by two generations of early Proterozoic granites at ca. 1.89–1.85 Ga and ca.1.82–1.78 Ga, respectively, and metamorphosed at upper amphibolite facies conditions. Small stratabound iron, copper, and zinc deposits occur in felsic to mafic tuffs and arkosic sediments. Small deposits of molybdenum, tungsten, and uranium formed during the emplacement of the younger granites. The lead isotopic compositions of sulfide trace lead from the various deposits are highly heterogeneous. In the 206Pb/204Pb–207Pb/204Pb diagram they fall on mixing arrays between little evolved early Proterozoic lead and highly radiogenic Caledonian lead. The least radiogenic lead isotopic compositions from the various deposits have a wide range of 207Pb/204Pb ratios and thus indicate variable involvement of Archaean crustal lead in the Proterozoic deposits. Deposits hosted by siliciclastic rocks have higher 207Pb/204Pb ratios than deposits hosted in mafic to felsic tuffites. The lead isotopic heterogeneity suggests that the lead in the various deposits was locally derived and, furthermore, that the sedimentary rocks in part originated from the Archaean craton to the north. Lead mixing arrays in the 206Pb/204Pb–207Pb/204Pb diagram demonstrate that in Paleozoic time radiogenic lead was mobilized and transported in the basement. Source ages calculated from the mixing arrays (ca.1.9 Ga and ca.1.8 Ga) correspond to the age of the Early Proterozoic volcanism and metamorphism respectively. One group of deposits includes lead from at least three sources and illustrates that radiogenic lead was multiply mobilized and transported in the Proterozoic basement. It occurs in deposits that occur in zones that became permeable during the reactivations of the basement.

Cavability investigation of a stratabound copper deposit, Tong Kuang Yu Mine, Shanxi Province, China : Lacy, W C Rock Mechanics as a Guide for Efficient Utilization of Natural Resources: Proc 30th U.S. Symposium, Morgantown, 19–22 June 1989P159–165. Publ Rotterdam: A A Balkema, 1989

Cavability investigation of a stratabound copper deposit, Tong Kuang Yu Mine, Shanxi Province, China : Lacy, W C Rock Mechanics as a Guide for Efficient Utilization of Natural Resources: Proc 30th U.S. Symposium, Morgantown, 19–22 June 1989P159–165. Publ Rotterdam: A A Balkema, 1989

Metallogeny and tectonic development of the Tasman Fold Belt System in New South Wales

The northwestern corner of New South Wales consists of the paratectonic Late Proterozoic to Early Cambrian Adelaide Fold Belt and older rocks, which represent basement inliers in this fold belt. The rest of the state is built by the composite Late Proterozoic to Triassic Tasman Fold Belt System or Tasmanides. In New South Wales the Tasman Fold Belt System includes three fold belts: (1) the Late Proterozoic to Early Palaeozoic Kanmantoo Fold Belt; (2) the Early to Middle Palaeozoic Lachlan Fold Belt; and (3) the Early Palaeozoic to Triassic New England Fold Belt. The Late Palaeozoic to Triassic Sydney—Bowen Basin represents the foredeep of the New England Fold Belt. The Tasmanides developed in an active plate margin setting through the interaction of East Gondwanaland with the Ur-(Precambrian) and Palaeo-Pacific plates. The Tasmanides are characterized by a polyphase terrane accretion history: during the Late Proterozoic to Triassic the Tasmanides experienced three major episodes of terrane dispersal (Late Proterozoic—Cambrian, Silurian—Devonian, and Late Carboniferous—Permian) and six terrane accretionary events (Cambrian—Ordovician, Late Ordovician—Early Silurian, Middle Devonian, Carboniferous, Middle-Late Permian, and Triassic). The individual fold belts resulted from one or more accretionary events. The Kanmantoo Fold Belt has a very restricted range of mineralization and is characterized by stratabound copper deposits, whereas the Lachlan and New England Fold Belts have a great variety of metallogenic environments associated with both accretionary and dispersive tectonic episodes. The earliest deposits in the Lachlan Fold Belt are stratabound Cu and Mn deposits of Cambro-Ordovician age. In the Ordovician Cu deposits were formed in a volcanic are. In the Silurian porphyry CuAu deposits were formed during the late stages of development of the same volcanic are. Post-accretionary porphyry CuAu deposits were emplaced in the Early Devonian on the sites of the accreted volcanic arc. In the Middle to Late Silurian and Early Devonian a large number of base metal deposits originated as a result of rifting and felsic volcanism. In the Silurian and Early Devonian numerous SnW, Mo and base metal—Au granitoid related deposits were formed. A younger group of MoW and Sn deposits resulted from Early—Middle Carboniferous granitic plutonism in the eastern part of the Lachlan Fold Belt. In the Middle Devonian epithermal Au was associated with rifting and bimodal volcanism in the extreme eastern part of the Lachlan Fold Belt. In the New England Fold Belt pre-accretionary deposits comprise stratabound Cu and Mn deposits (pre-Early Devonian): stratabound Cu and Mn and ?exhalite Au deposits (Late Devonian to Early Carboniferous); and stratabound Cu, exhalite Au, and quartz—magnetite (?Late Carboniferous). S-type magmatism in the Late Carboniferous—Early Permian was responsible for vein Sn and possibly AuAsAgSb deposits. Volcanogenic base metals, when compared with the Lachlan Fold Belt, are only poorly represented, and were formed in the Early Permian. The metallogenesis of the New England Fold Belt is dominated by granitoid-related mineralization of Middle Permian to Triassic age, including SnW, MoW, and AuAgAs Sb deposits. Also in the Middle Permian epithermal AuAg mineralization was developed. During the above period of post-orogenic magmatism sizeable metahydrothermal SbAu(W) and Au deposits were emplaced in major fracture and shear zones in central and eastern New England. The occurrence of antimony provides an additional distinguishing factor between the New England and Lachlan Fold Belts. In the New England Fold Belt antimony deposits are abundant whereas they are rare in the Lachlan Fold Belt. This may suggest fundamental crustal differences.

Regional controls on the localisation of stratabound copper deposits: Proterozoic examples from southern Africa and south Australia

A comparative study of three areas containing stratabound copper deposits was conducted in order to evaluate possible regional controls on the localisation of stratabound copper deposits. The areas studied are: (1) Klein Aub in SWA/Namibia, where deposits are hosted by dark argilites in the Upper Proterozoic Sinclair Sequence; (2) Alaska and Mhangura in Zimbabwe, where deposits are hosted by argillites, arkoses and conglomerates in the Middle Proterozoic Deweras Group; (3) Mount Gunson in South Australia, where deposits are hosted by siltstones, sandstones and breccias in the Upper Proterozoic Adelaidean Sequence of the Stuart Shelf. In all cases the tectonic setting is intracratonic or epicratonic, which results in an overall similarity of lithologies in the three regions. The sequences are dominated by medium to coarse, red coloured clastic sediments. Dark carbonaceous shales, evaporites and basin volcanics are present in all the areas studied, and may be genetically important. There is no consistency in host rock lithology or host rock depositional environment. Marine transgressions and disconformities may be important in some instances, but are not generally controlling factors. Klein Aub, Alaska, and Mhangura occur near basin margins, but this is not the case with Mount Gunson. A feature common to all three areas is sedimentary onlap of the copper-bearing sequences onto a basement high. Structural controls are difficult to evaluate, but the basement rocks are block faulted and the basement highs are probably horst blocks. Basement faults may continue through into the host rock sequences as synsedimentary (growth) faults which controlled the development of depositional sub-basins and hence controlled the distribution of lithologies and mineralisation.