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1.
The Alvo 118 iron oxide–copper–gold (IOCG) deposit (170 Mt at 1.0 wt.% Cu, 0.3 g/t Au) lies in the southern sector of the Itacaúnas Shear Belt, Carajás Mineral Province, along a WNW–ESE-striking, 60-km-long shear zone, close to the contact of the ~2.76-Ga metavolcano-sedimentary Itacaiúnas Supergroup and the basement (~3.0 Ga Xingu Complex). The Alvo 118 deposit is hosted by mafic and felsic metavolcanic rocks and crosscutting granitoid and gabbro intrusions that have been subjected to the following hydrothermal alteration sequence towards the ore zones: (1) poorly developed sodic alteration (albite and scapolite); (2) potassic alteration (biotite or K-feldspar) accompanied by magnetite formation and silicification; (3) widespread, pervasive chlorite alteration spatially associated with quartz–carbonate–sulphide infill ore breccia and vein stockworks; and (4) local post-ore quartz–sericite alteration. The ore assemblage is dominated by chalcopyrite (~60%), bornite (~10%), hematite (~20%), magnetite (10%) and subordinate chalcocite, native gold, Au–Ag tellurides, galena, cassiterite, F-rich apatite, xenotime, monazite, britholite-(Y) and a gadolinite-group mineral. Fluid inclusion studies in quartz point to a fluid regime composed of two distinct fluid types that may have probably coexisted within the timeframe of the Cu–Au mineralizing episode: a hot (>200°C) saline (32.8‰ to 40.6 wt.% NaCl eq.) solution, represented by salt-bearing aqueous inclusions, and a lower temperature (<200°C), low to intermediate salinity (<15 wt.% NaCl eq.) aqueous fluid defined by two-phase (LH2O + VH2O) fluid inclusions. This trend is very similar to those defined for other IOCG systems of the Carajás Mineral Province. δ 18OH2O values in equilibrium with calcite (−1.0‰ to 7.5‰ at 277°C to 344°C) overlap the lower range for primary magmatic waters, but the more 18O-depleted values also point to the involvement of externally derived fluids, possibly of meteoric origin. Furthermore, sulphide δ 34S values (5.1‰ to 6.3‰), together with available boron isotope and Cl/Br–Na/Cl data provide evidence for a significant component of residual evaporative fluids (e.g., bittern fluids generated by seawater evaporation) in this scenario that, together with magma-derived brines, would be the main sources of the highly saline fluids involved in the formation Alvo 118 IOCG deposit. The restricted high temperature sodic alteration, the pervasive overprinting of the potassic alteration minerals by chlorite proximal to the ore zones, ore breccias with open-space filling textures in brittle structures, microthermometric and stable isotope data indicate, collectively, that the Alvo 118 IOCG system developed at structurally high levels and may be considered the shallower representative of the IOCG systems of the CMP.  相似文献   

2.
The Upper Jurassic Mantos Blancos copper deposit (500 Mt at 1.0% Cu), located in the Coastal Range of northern Chile, displays two superimposed hydrothermal events. An older phyllic alteration probably related to felsic magmatic–hydrothermal brecciation at ∼155 Ma, and younger (141–142 Ma) potassic, propylitic, and sodic alterations, coeval with dioritic and granodioritic stocks and sills, and dioritic dikes. Main ore formation is genetically related to the second hydrothermal event, and consists of hydrothermal breccias, disseminations and stockwork-style mineralization, associated with sodic alteration. Hypogene sulfide assemblages show distinctive vertical and lateral zoning, centered on magmatic and hydrothermal breccia bodies, which constitute the feeders to mineralization. A barren pyrite root zone is overlain by pyrite-chalcopyrite, and followed upwards and laterally by chalcopyrite-digenite or chalcopyrite-bornite. The assemblage digenite–supergene chalcocite characterizes the central portions of high-grade mineralization in the breccia bodies. Fluid inclusions show evidence of boiling during the potassic and sodic alteration events, which occurred at temperatures around 450–460°C and 350–410°C, and salinities between 3–53 and 13–45 wt% NaCl eq., respectively. The hydrothermal events occurred during episodic decompression due to fluid overpressuring, hydrofracturing, and sharp changes from lithostatic to hydrostatic conditions. Sulfur isotope results of hypogene sulfide minerals fall in a narrow range around 0 per mil, suggesting a dominance of magmatic sulfur. Carbon and oxygen isotopic data of calcites from propylitic alteration suggest a mantle-derived carbon and oxygen isotope fractionation due to low-temperature alteration.  相似文献   

3.
Major Cu–Au deposits of iron oxide–copper–gold (IOCG) style are temporally associated with oxidized, potassic granitoids similar to those linked to major porphyry Cu–Au deposits. Stable and radiogenic isotope evidence indicates fluids and ore components were likely sourced from the intrusions. IOCG deposits form over a range of crustal levels because CO2-rich fluids separate from the magmas at higher pressures than in CO2-poor systems, thereby, promoting partitioning of H2O, Cl and metals to the fluid phase. At deep levels, the magma–fluid system cannot generate sufficient mechanical energy to fracture the host rocks as in porphyry systems and the IOCG deposits therefore form in a variety of fault-related structural traps where the magmatic fluids may mix with other fluids to promote ore formation. At shallow levels, the IOCG deposits form breccia and fracture-hosted mineralization styles similar to the hydrothermal intrusive breccias and sulphide vein systems that characterize many porphyry Cu–Au deposits. The fluids associated with IOCG deposits are typically H2O–CO2–salt fluids that evolve by unmixing of the carbonic phase and by mixing with fluids from other sources. In contrast, fluids in porphyry systems typically evolve by boiling of moderate salinity fluid to produce high salinity brine and a vapor phase commonly with input of externally derived fluids. These different fluid compositions and mechanisms of evolution lead to different alteration types and parageneses in porphyry and IOCG deposits. Porphyry Cu–Au deposits typically evolve through potassic, sericitic and (intermediate and/or advanced) argillic stages, while IOCG deposits typically evolve through sodic(–calcic), potassic and carbonate-rich stages, and at deeper levels, generally lack sericitic and argillic alteration. The common association of porphyry and IOCG Cu–Au deposits with potassic, oxidized intermediate to felsic granitoids, together with their contrasting fluid compositions, alteration styles and parageneses suggest that they should be considered as part of the broad family of intrusion-related systems but that they are typically not directly related to each other.  相似文献   

4.
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% NaCleq 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.  相似文献   

5.
十二排钼矿床位于上杭-云霄断裂带与闽西南拗陷的复合部位,是紫金山铜金矿田外围新近探明的一处具有中大型远景的斑岩型钼矿床。野外地质调查显示,其钼矿化呈细脉状、网脉状主要产出于黑云母二长花岗岩和黑云母花岗斑岩中。热液蚀变具有斑岩型矿床的分带特征,由黑云母花岗斑岩向外依次发育钾硅酸盐化带、绢英岩化带和青磐岩化带,钼矿体主要赋存于绢英岩化与钾硅酸盐化构成的叠加带中。锆石U-Pb定年结果表明,黑云母二长花岗岩和黑云母花岗斑岩分别形成于(143.1±0.9)Ma和(143.5±0.4)Ma。4件辉钼矿样品的Re-Os加权平均年龄为(143.9±2.1)Ma。辉钼矿的w(Re)为1.2×10~(-6)～7.8×10~(-6),说明成矿物质可能主要来自地壳。岩石地球化学分析结果显示,十二排含矿花岗岩具有相似的主量和微量元素组成,均属于弱过铝质高钾钙碱性I型花岗岩,其中,黑云母花岗斑岩表现出高分异花岗岩特征,两者可能是古老变质基底来源的熔体经历不同程度分异结晶的产物,并混入有少量幔源物质。综合已有的资料,文章认为十二排斑岩型钼矿化与早白垩世早期花岗质岩浆活动密切相关,上杭-云霄断裂带存在古太平洋板块俯冲后撤引发构造体制转换阶段的成岩成矿响应,进一步找矿勘查工作应加强评价早白垩世早期高分异花岗岩体的钼多金属成矿潜力。  相似文献   

6.
Uranium and polymetallic U mineralization hosted within brecciated albitites occurs one kilometer south of the magnetite-rich Au–Co–Bi–Cu NICO deposit in the southern Great Bear magmatic zone (GBMZ), Canada. Concentrations up to 1 wt% U are distributed throughout a 3 by 0.5 km albitization corridor defined as the Southern Breccia zone. Two distinct U mineralization events are observed. Primary uraninite precipitated with or without pyrite–chalcopyrite?±?molybdenite within magnetite–ilmenite–biotite–K-feldspar-altered breccias during high-temperature potassic–iron alteration. Subsequently, pitchblende precipitated in earthy hematite–specular hematite–chlorite veins associated with a low-temperature iron–magnesium alteration. The uraninite-bearing mineralization postdates sodic (albite) and more localized high-temperature potassic–iron (biotite–magnetite ± K-feldspar) alteration yet predates potassic (K-feldspar), boron (tourmaline) and potassic–iron–magnesium (hematite ± K-feldspar ± chlorite) alteration. The Southern Breccia zone shares attributes of the Valhalla (Australia) and Lagoa Real (Brazil) albitite-hosted U deposits but contains greater iron oxide contents and lower contents of riebeckite and carbonates. Potassium, Ni, and Th are also enriched whereas Zr and Sr are depleted with respect to the aforementioned albitite-hosted U deposits. Field relationships, geochemical signatures and available U–Pb dates on pre-, syn- and post-mineralization intrusions place the development of the Southern Breccia and the NICO deposit as part of a single iron oxide alkali-altered (IOAA) system. In addition, this case example illustrates that albitite-hosted U deposits can form in albitization zones that predate base and precious metal ore zones in a single IOAA system and become traps for U and multiple metals once the tectonic regime favors fluid mixing and oxidation-reduction reactions.  相似文献   

7.
The large Vorontsovskoe Au-Hg-As deposit in the Urals is located in the exocontact of the Early Devonian Auerbah gabbro-diorite-granodiorite massif, which intrudes volcano-sedimentary rocks. The orebodies are confined to a tectonic contact of calcareous and tuffaceous rocks. They are composed of 6 types of disseminated ores, but the main reserves of gold are associated with the following ore types: gold-pyrite-arsenopyrite in altered tuffaceous rocks, pyrite-realgar ores in limestone breccia with a carbonate-volcanogenic cement, and gold-oxide-clay from regolith with residual gold. Early ore associations have been formed at 450–300 °C, whereas the late ores have been formed at lower temperature of 260–110 °C. We propose a model for the genesis of the Vorontsovskoe deposit based on synchronicity of mineralization with the formation of the Auerbah volcano-plutonic complex. The Ar-Ar age of hydromica from the gold-arsenopyrite association is 391.1 ± 4.9 Ma, which coincides with the age of igneous rocks of the Auerbah complex. The main sources of water and carbon dioxide were composed of the fluid derived from the magma chamber and the metamorphic water equilibrated with carbonate sedimentary rocks. Magmatic fluid dominated during the development of skarns, jasperoids and quartz veins, whereas metamorphic water was dominant during quartz-sericite alteration of volcano-sedimentary rocks and calcareous breccias. The bulk of the sulfur was supplied by a deep magma reservoir, however this source prevailed only during skarn ore formation. The mixing between deep-sourced sulfur and sedimentary or biogenic sulfur was established for other ore types. Gold and other ore components were possibly introduced during the volcanic and intrusive activity and also extracted from host sedimentary rocks.  相似文献   

8.
The breccia-hosted epithermal gold–silver deposit of Chah Zard is located within a high-K, calc-alkaline andesitic to rhyolitic volcanic complex in the central part of the Urumieh-Dokhtar Magmatic Arc (UDMA), west central Iran. The total measured resource for Chah Zard is ∼2.5 million tonnes of ore at 12.7 g/t Ag and 1.7 g/t Au (28.6 t Ag, 3.8 t Au), making it one of the largest epithermal gold deposits in Iran. Magmatic and hydrothermal activity was associated with local extensional tectonics in a strike-slip regime formed in transtensional structures of the Dehshir-Baft strike-slip fault system. The host rocks of the volcanic complex consist of Eocene sedimentary and volcanic rocks covered by Miocene sedimentary rocks. LA-ICP–MS U–Pb zircon geochronology yields a mean age of 6.2 ± 0.2 Ma for magmatic activity at Chah Zard. This age represents the maximum age of mineralization and may indicate a previously unrecognized mineralization event in the UDMA. Breccias and veins formed during and after the waning stages of explosive brecciation events due to shallow emplacement of rhyolite porphyry. Detailed systematic mapping leads to the recognition of three distinct breccia bodies: volcaniclastic breccia with a dominantly clastic matrix; gray polymict breccia with a greater proportion of hydrothermal cement; and mixed monomict to polymict breccia with clay matrix. The polymictic breccias generated bulk-mineable ore, whereas the volcaniclastic breccia is relatively impermeable and largely barren. Precious metals occur with sulfide and sulfosalt minerals as disseminations, as well as in the veins and breccia cements. There is a progression from pyrite-dominated (stage 1) to pyrite-base metal sulfide and sulfosalt-dominated (stages 2 and 3) to base metal sulfide-dominated (stage 4) breccias and veins. Hydrothermal alteration and deposition of gangue minerals progressed from illite-quartz to quartz-adularia, carbonate, and finally gypsum-dominated assemblages. Free gold occurs in stages 2 and 4, principally intergrown with pyrite, quartz, chalcopyrite, galena, sphalerite, and Ag-rich tennantite–tetrahedrite, and also as inclusions in pyrite. High Rb/Sr ratios in ore-grade zones are closely related to sericite and adularia alteration. Positive correlations of Au and Ag with Cu, As, Pb, Zn, Sb, and Cd in epithermal veins and breccias suggest that all these elements are related to the same mineralization event.  相似文献   

9.
铜厂铜-铁矿床是勉略宁矿集区具有代表性的矿床之一,主要由上部的铜厂铜矿床和下部的杨家坝铁矿床(铜厂铁矿床)组成。根据磁铁矿和硫化物的相对含量,铜厂铜-铁矿床的矿石可分为磁铁矿矿石、含硫化物磁铁矿矿石和硫化物矿石三类。系统的岩相学和矿相学研究表明,其矿石矿物主要为磁铁矿、黄铜矿、黄铁矿和磁黄铁矿;矿石结构包括自形-半自形-他形粒状结构、交代残余结构和包含结构,矿石构造包括块状、浸染状、脉状和条带状构造。铜厂铜-铁矿床的围岩蚀变种类较多,且具有一定的分带性,上部铜矿体围岩蚀变以硅化、碳酸盐化和黑云母化为主,以石英、方解石和黑云母为主的蚀变矿物组合显示钾化特征;下部铁矿体围岩蚀变有钠长石化、蛇纹石化、滑石化、透闪石化、碳酸盐化、绿泥石化等,以钠长石、蛇纹石、滑石、透闪石、方解石、白云石、菱铁矿、绿泥石、黑云母和磷灰石等为主的蚀变矿物组合显示钠化特征。铜厂铜-铁矿床中磁铁矿的TiO2含量小于1.72%,Al2O3含量小于1.81%,均显示热液磁铁矿的特征,结合铜矿石脉穿插铜厂闪长岩及二者突变接触的地质特征,说明铜厂铜-铁矿床的形成与热液活动密切相关。同时,铜厂铜-铁矿床形成于早古生代加里东期,勉略宁矿集区在该时期处于大陆裂谷的扩张环境中,与铁氧化物-铜-金(Iron Oxide-Copper-Gold,简称IOCG)矿床的形成环境类似。通过与典型IOCG矿床地质特征、矿化蚀变特征、矿物组合特征、矿物地球化学特征及大地构造背景的系统对比,初步提出铜厂铜-铁矿床应属于IOCG矿床。  相似文献   

10.
A large scale Proterozoic breccia system consisting of numerous individual breccia bodies, collectively known as Wernecke Breccia, occurs in north-central Yukon Territory, Canada. Breccias cut Early Proterozoic Wernecke Supergroup sedimentary rocks and occur throughout the approximately 13 km thick deformed and weakly metamorphosed sequence. Iron oxide–copper–gold ± uranium ± cobalt mineralization is associated with the breccia bodies and occurs as veins and disseminations within breccia and surrounding rocks and locally forms the breccia matrix. Extensive sodic and potassic metasomatic alteration occurs within and around breccia bodies and is overprinted by pervasive calcite and dolomite/ankerite, and locally siderite, alteration, respectively. Multiple phases of brecciation, alteration and mineralization are evident. Breccia bodies are spatially associated with regional-scale faults and breccia emplacement made use of pre-existing crustal weaknesses and permeable zones. New evidence indicates the presence of metaevaporitic rocks in lower WSG that may be intimately related to breccia formation. No evidence of breccia-age magmatism has been found to date.
Julie HuntEmail:
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