论与斑岩矿床有关的矿化角砾岩成因类型及其地质意义

伴随有各类矿化角砾岩的斑岩矿床是深成源岩在浅成-超浅成条件下侵位-矿化的产物。本文详细阐述了与斑岩矿床有关的各类矿化角砾岩的地质特征、成因分类和识别标志,并从中国独特的构造环境出发,对与矿化角砾岩有关的各种地质现象作了初步剖析,指出矿化角砾岩的形成从根本上讲是深成岩浆侵位的多旋回性造成的,以岩浆水为主体的热流体是含矿斑岩体系从封闭环境转为开放环境的主要动力条件。因此,矿化角砾岩不仅是金属元素的原始富集条件,而且是重要的找矿标志之一。我国与斑岩矿床有关的矿化角砾岩的主要成因类型为爆破角砾岩、侵入角砾岩、火山角砾岩等。多种角砾岩的叠加现象十分明显,热液交代角砾岩的叠加作用为矿化过程的指示标志.     

Fluidization： An Important Process in the Formation of the Qiyugou Au-bearing Breccia Pipes in Central China

Fluidization processes based on experiments are reviewed to gain some useful insights and comparisons with those that occur in hydrothermal systems. Field and petrographic work, and microscope observation were carried out on samples from the Qiyugou Au-bearing breccia pipes from the East Qinling region, Henan Province. Evidence from macro- and micro-textures suggests that the style of breccias in the Qiyugou area can be grouped into three types： （1） jigsaw fit-stockwork texture, in which the interval between clasts is marked by fractures or filled with calcite or quartz veins; （2） larger breccias that are supported by smaller breccias, rock flour and alteration materials; in this type clasts moved over short distances, creating open spaces; （3） fluidized texture, where the clasts of different lithologies have rounded shapes. These observations are compared with those resulting from experiments on fluidization processes. The results of this comparison suggest that fluidization is an important geological process in the formation of the Qiyugou Au-bearing breccia pipes and gold mineralization. In addition, fluidization processes such as expansion, bubbling, slugging, channeling and spouting must have contributed to the formation of the pipes and were conducive to the development of gold mineralization. In the Qiyugou breccia pipes, gold mineralization occurs as disseminations, in stockwork veins, and open space infills. The ore zones form subparallel sheets that are nearly perpendicular to the walls of the pipes.     

西藏东部隐爆角砾岩特征及其含矿性

西藏东部发育大量与喜马拉雅期斑岩密切共生的隐爆角砾岩筒(脉)。隐爆角砾岩大都遭受强烈的矿化蚀变，其中的成矿元素金、银、汞等强烈富集。包裹体和同位素的资料证实爆破流体是一种与岩浆有成因联系的、介于岩浆与岩浆期后成矿热液之间的过渡性高温流体。     

Geology and geochronology of Naruo large porphyry-breccia Cu deposit in the Duolong district,Tibet

The Duolong district is located in the south Qiangtang terrane of Tibet and is the most significant ore cluster within the Bangongco-Nujiang metallogenic belt. Duolong contains one giant, three large and two medium to small-sized porphyry (±epithermal ± breccia) copper deposits and several other mineralized porphyry bodies. All deposits are closely associated with early Cretaceous (123–115 Ma) intermediate-felsic intrusions. Naruo is a poorly studied porphyry-breccia copper deposit in the north of the Duolong district. Hydrothermal alteration surrounding the ore-bearing granodiorite at Naruo is characterized by an inner potassic zone and an outer propylitic zone, overlapped locally by minor phyllic and argillic alteration assemblages. A detailed paragenetic study has identified five distinct hydrothermal veins (M, A, B, C, D) within the porphyry system. Hydrothermal B veins are strongly related to copper mineralization. Strong propylitic alteration is also observed throughout the hydrothermal breccias identified at Naruo. Sandstone breccia, diorite-bearing breccia and granodiorite-bearing breccia were identified according to the distribution and composition of clasts. U-Pb zircon dating has determined the ages of the ore-bearing granodiorite (121.6 ± 1.3 Ma) and a barren intrusion (115.5 ± 1.1 Ma) within the porphyry system, diorite clasts (122.3 ± 0.9 Ma) and later diorite matrix (120.5 ± 1.0 Ma) in the hydrothermal breccia system, suggesting that with the exception of the late barren intrusion, they all belong to the same mineralizing event at Duolong. The geological and geochemical evidence presented in this study suggest that the porphyry and breccia systems may have originated from the same magma source, but are now spatially independent.     

Geology of the High Sulfidation Copper Deposits,Monywa Mine,Myanmar

The 50 km² Monywa copper district lies near the Chindwin River within the northward continuation of the Sunda‐Andaman magmatic arc through western Myanmar. There are four deposits; Sabetaung, Sabetaung South, Kyisintaung, and the much larger Letpadaung 7 km to the southeast. Following exploration drilling which began in 1959, production of copper concentrates from a small open pit started at Sabetaung in 1983. Since 1997, when resources totaled 7 million tonnes contained copper in 2 billion tonnes ore, a heap leach–electro‐winning operation has produced over 400,000 t copper cathode from Sabetaung and Sabetaung South. Ore is hosted by mid‐Miocene andesite or dacite porphyry intrusions, and by early mid‐Miocene sandstone and overlying volcaniclastics including eruptive diatreme facies which the porphyries intrude. District‐wide rhyolite dykes and domes with marginal breccias probably post‐date andesite porphyries in the mine area and lack ore‐grade copper. Host rocks to mineralization are altered to phyllic and advanced argillic hydrothermal assemblages within an outer chlorite zone; hypogene alunite is most abundant at Letpadaung and Kyisintaung. Most mineralization is structurally‐controlled with digenite‐chalcocite in breccia dykes, in steeply dipping NE‐trending sheeted veins, and in stockwork and low‐angle sulfide veins. A high‐grade pipe at Sabetaung grades up to 30% Cu, and much of the ore at Sabetaung South is in a NE‐trending zone of mega‐breccia and stockworked sandstone. The hydrothermal alteration, together with replacement quartz, alunite and barite in breccia dykes and veins, the virtual absence of vein quartz, and the presence of chalcopyrite and bornite only as rare veins and as inclusions within the abundant pyrite, indicate that the deposits are high sulfidation. Regional uplift, resistance to erosion and leaching of the altered and mineralized rocks have resulted in porous limonite‐stained leached caps over 200 m thick forming the Letpadaung and Kyisintaung hills. The barren caps pass abruptly downwards at the water table into the highest grade ore at the top of the supergene enrichment zone, within which copper grade, supergene kaolinite and cubic alunite decrease, and pyrite increases with depth; in contrast, marcasite is mostly shallow. Much of the copper to depths exceeding 200 m below the water table occurs as supergene digenite‐chalcocite and minor covellite. Disseminated chalcocite is mostly near‐surface and hence almost certainly supergene. We infer that during prolonged uplift at all four deposits, oxidation of residual pyrite at the water table generated enough acid to leach all the copper from earlier supergene‐enriched ore; below the water table the resulting acid sulfate solutions partly replaced enargite, covellite, chalcopyrite, bornite and pyrite with supergene chalcocite. Undeformed upward‐fining cross‐bedded conglomerates and sands of the ancestral Chindwin River floodplain overlie the margins of the Sabetaung deposits, form a major aquifer up to 40 m thick, and are a potential host for exotic copper mineralization. A mid‐Miocene pluton is inferred to underlie the Monywa deposits, but the possibility of porphyry‐type mineralization within the district is at best highly speculative.     

The Donoso copper-rich,tourmaline-bearing breccia pipe in central Chile: petrologic,fluid inclusion and stable isotope evidence for an origin from magmatic fluids

The copper-rich, tourmaline-bearing Donoso breccia pipe is one among more than 15 different mineralized breccias in the giant (>50 million metric tonnes of copper) Miocene and Pliocene Río Blanco-Los Bronces copper deposit in the high Andes of central Chile. This breccia pipe, bracketed in age between 5.2 and 4.9 Ma, has dimensions of 500 by 700 m at the current surface 3,670 m above sea level. Its roots have yet to be encountered, and it is >300 m in diameter at the depth of the deepest drill holes. The Donoso breccia is, for the most part, monolithic, containing clasts of the equigranular quartz monzonite pluton which hosts the pipe. It is matrix supported, with between 5 and 25% of the total rock volume consisting of breccia-matrix minerals, which include tourmaline, quartz, chalcopyrite, pyrite, specularite, and lesser amounts of bornite and anhydrite. An open pit mine, centered on this breccia pipe, has a current production of 50,000 tonnes of ore per day at an average grade of 1.2% copper, and copper grade in the breccia matrix is significantly higher. Measured '¹⁸O for tourmaline and quartz from the matrix of the Donoso breccia at different levels of the pipe range from +6.9 to +12.0‰, and measured 'D in tourmaline ranges from -73 to -95‰. Temperatures of crystallization of these minerals, as determined by the highest homogenization temperatures of highly saline fluid inclusions, range from 400 to >690°C. When corrected for these temperatures, the stable isotope data indicate that fluids from which these breccia-matrix minerals precipitated were magmatic, with '¹⁸O between +5.6 to +9.1‰ and 'D between -51 to -80‰. These isotopic data preclude participation of a significant amount of meteoric water in the formation of the Donoso breccia. They support a model in which brecciation is caused by expansion of magmatic fluids exsolved from a cooling pluton, and breccia-matrix minerals, including copper sulfides, precipitated from the same magmatic fluids responsible for brecciation. Sericitic alteration of clasts in the breccia was also caused by these magmatic fluids. Different types of fluid inclusions imply that several different magmatic fluids were involved in formation of the Donoso breccia. These include high-temperature, highly saline, non-boiling fluids, trapped in inclusions that homogenize by halite dissolution, which probably exsolved from a magma cooling under relatively high (>1 kbar) lithostatic pressure conditions, consistent with geologic constraints. Other high-temperature, highly saline fluids are trapped in inclusions that homogenize by vapor-bubble disappearance and are spatially associated with vapor-rich inclusions, suggesting either phase separation (boiling) or simultaneous separation of immiscible brine and vapor from a magma cooling at lower hydrostatic pressure conditions. Both types of high-temperature, highly saline fluids circulated intermittently, as pressure fluctuated between lithostatic and hydrostatic conditions because of episodes of sealing and rebrecciation.     

祁雨沟含金角砾岩筒中的冰长石-方解石组合及其矿床地质意义

通过野外地质、岩相学、拉曼光谱和电子探针分析，对祁雨沟2号和4号含金角砾岩筒中冰长石-方解石蚀变矿物组合特征进行了描述。含金角砾岩筒成矿作用分为两期：面状矿化和脉状矿化。面状矿化的蚀变主要有阳起石化、绿色黑云母化、绿泥石化、冰长石化、硅化、绿帘石化、黄铁矿化、碳酸盐化和少量的绢云母化。脉状矿化蚀变为硅化、绢云母化和少量的碳酸盐化。通过对角砾岩筒的蚀变与成矿作用关系研究，认为冰长石-方解石蚀变与含金角砾岩金成矿作用是同期，从而确定祁雨沟含金角砾岩筒是一个典型的低硫型浅成低温热液型金矿床。     

安徽宣城茶亭铜金矿床隐爆角砾岩特征及其成矿意义

安徽宣城茶亭铜金矿床是近年来在长江中下游浅覆盖区之南陵—宣城中—新生代火山—沉积盆地中新发现的一个大型矿床。文章以赋矿石英闪长玢岩侵入体内发育的隐爆角砾岩为对象,通过详细的钻孔岩心观察和显微岩相学研究,确定其地质特征并探讨其与成矿的关系。根据钻孔岩心观察确定的岩石构造特征及钻孔剖面圈定的角砾岩空间分布特征,茶亭铜金矿床发育的隐爆角砾岩呈上大下小的不规则筒状体,被隐伏的石英闪长玢岩侵入体包孕。根据角砾特征以及角砾间的裂隙和胶结物特征,可将隐爆角砾岩划分为隐爆浆屑角砾岩、隐爆热液角砾岩和隐爆破裂角砾岩三类,三类隐爆角砾岩空间上有规律地分布,以隐爆浆屑角砾岩为中心向外或向上依次过渡为隐爆热液角砾岩→隐爆破裂角砾岩→石英闪长玢岩。基于隐爆角砾岩与蚀变和矿化的关系推测,岩浆—气液隐蔽爆破作用所产生的大量裂隙为后期含矿岩浆热液和大气降水热液的运移、交代、混合乃至卸载、沉淀成矿提供了有利的构造空间。茶亭铜金矿床的矿体赋存于浅成斑岩侵入体中,其围岩蚀变类型与分带,以及矿化呈细粒浸染状和细脉—网脉状等地质特征显示其与斑岩型矿床极为相似,但矿化富集部位与隐爆角砾岩筒（体） 的一致,且矿床同时发育角砾状、脉状、团块状矿化,矿脉中发育热液硬石膏甚至形成硬石膏岩等地质特征又明显不同于斑岩型矿床。因此,文章将茶亭铜金矿床确定为一个与中酸性浅成斑岩侵入体密切相关的隐爆角砾岩型矿床。     

Iron oxide copper-gold (IOCG) mineralization at the Imiter inlier,Eastern Anti-Atlas,Morocco

The Imiter inlier at the eastern Anti-Atlas chain (Morocco) hosts a world-class epithermal Ag-Hg deposit, and several occurrences of sulfide-magnetite mineralization. These occurrences are confined to transcurrent faults that cut mildly to highly potassic I- and S-type granite intrusions (e.g., Igoudrane, Bou Teglimt, Taouzzakt and Bou Fliou).In this contribution, we present new field, petrographic and microanalytical data of the Bou Fliou sulfide-magnetite mineralization in the northwestern part of the Bou Teglimt granodiorite intrusion (567?±?6Ma). Field and microscopic investigations reveal pervasive silicification and potassic alteration associated with iron oxides-rich (>10?vol %) veins, stockworks, and breccias along NE-SW faults. The ore minerals are mainly magnetite, hematite, chalcopyrite, pyrite, sphalerite, Ag-galena, cobaltite, and less abundant Bi-sulfosalts (i.e., cosalite, galenobistmuthite, and llilanite-gustavite). The low-titanium iron oxides (magnetite and hematite), widespread iron-rich breccia, association with crustal scale fault zone, pervasive alteration, and overprinting mineral assemblages suggest a shallow level IOCG-style mineralization. High-order splays of the major fault zone could have provided effective traps for magmatic and basinal Cu and Zn-Pb hydrothermal fluids. The ～550 Ma intrusive phases in the region could have contributed by fluid, elements or heat in a local effective blumbing. The mineralogical and ore textural criteria reflecting ore formation at a realtively shallow crustal environment, but a fluid inclusion study is needed to characterize the ore fluids and mechanism of ore deposition.     

Geological setting and timing of the Chah Zard breccia-hosted epithermal gold–silver deposit in the Tethyan belt of Iran

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.     

Porphyry to epithermal transition in the Agua Rica polymetallic deposit, Catamarca, Argentina: An integrated petrologic analysis of ore and alteration parageneses

Agua Rica (27°26′S–66°16′O) is a world class Cu–Au–Mo deposit located in Catamarca, Argentina. In the E–W 6969400 section examined, the Seca Norte and the Trampeadero porphyries that have intruded the metasedimentary rock are cut by interfingered igneous and hydrothermal heterolithic and monolithic breccias, and sandy dikes. Relic biotite and K-feldspar of the early potassic alteration (370° to > 550 °C) with Cu (Mo–Au) mineralization are locally preserved and encapsulated in a widespread, white mica + quartz + rutile or anatase halo (phyllic alteration) with pyrite + covellite that suggests fluids with temperatures ≤ 360 °C and high f(S₂). The Trampeadero porphyry and the surrounding metasedimentary rock with phyllic alteration have molybdenite in stringers and B-type quartz veinlets and the highest Mo grades (> 1000 ppm).Multistage advanced argillic alteration overprinted the earlier stages. Early andalusite ± pyrite ± quartz is preserved in the roots of the argillic halo rimmed by an alumina–silica material and white micas. This alteration assemblage is considered to have been formed at temperatures ≥ 375 °C from condensed magmatic vapor. At higher levels, pyrophyllite replaces muscovite and illite in clasts of hydrothermal breccias in the center and east sector of the study section, suggesting temperatures of 280 to 360 °C. Clasts of vuggy silica in the uppermost levels of the central breccia, indicates that at lower temperatures (< 250 °C), fluids reached very low pH (pH < 2). In this early stage of the advanced argillic alteration, hydrothermal fluids seem to have not precipitated sulfides or sulfosalts.Hydrothermal brecciation was concurrent with fluid exsolution (↑? V), which precipitated intermediate-temperature advanced argillic alunite (svanbergite + woodhouseite) ± diaspore ± zunyite as breccia cement along with abundant covellite + pyrite + enargite ± native sulfur ± kuramite at intermediate depths and in lateral transitional zones to unbrecciated rocks. This mineral assemblage indicates temperatures near 300 °C, oxidized and silica-undersaturated hydrothermal fluids with high sulfur fugacity to prevent gold precipitation. Multiple generations of pyrite, emplectite, colusite, Pb- and Bi-bearing sulfosalts, and native sulfur with Au and Ag, accompanied by alunite introduction in the upper level breccias, probably occurred at lower temperatures, but still high sulfur and oxygen activity. An independent Zn and Pb (as galena) mineralization stage locally coincides with Au–Ag and sulfosalts, and advanced at depth, controlled by fractures and overprinting much of the previous mineralization. A later paragenesis of veinlets of alunite + woodhouseite + svanvergite + pyrite ± enargite that cut the phyllic halo suggests temperatures ~ 250 °C and without woodhouseite + svanvergite, temperatures ~ 200 °C. Kaolinite occurs in the phyllic halo as a late mineral in clots and in veinlets thus, in this zone, the fluid had cooled enough for its formation.     

Geological development and mineralization in the Atacama segment of the South American Andes,northern Chile (26°15′–27°25′S)

Between the Late Jurassic and the Middle Miocene, widespread magmatism, tectonic events and hydrothermal mineralization characterized the geological evolution of the Atacama segment of the South American Andes. A characteristic feature of this zone is the coincidence in time and space between subduction-generated igneous activity, crustal deformation and mineralization in the magmatic arcs, which formed longitudinal belts migrating eastward.Mineralization in the last 140 Ma is generally restricted to four longitudinal metallogenic belts, in which hydrothermal activity was channelled along crustal-scale faults (1) the Atacama Fault System, along which Early Cretaceous Cu-Au-bearing breccia pipes, veins and stockwork were formed; (2) the Inca do Oro Belt, which contains Upper Cretaceous low sulphur precious metal epithermal mineralization, and Middle Eocene Cu-Mo-Au-bearing breccia pipes; (3) the West Fissure System, which hosts Upper Eocene to Early Oligocene porphyry copper deposits and high sulphur precious metal epithermal mineralization; and (4) the Maricunga Belt, when contains Upper Oligocene to Middle Miocene high sulphur precious metal epithermal deposits and Au-rich porphyry mineralization.     

Characteristics of Breccias and C-O-Sr-S Isotope Geochemistry of the Duocaima Pb-Zn Deposit in Tuotuohe, Qinghai Province: Implications for the Ore-forming Process

The Duocaima carbonate-hosted Pb-Zn deposit is a newly found large deposit in the southern area of Qinghai Province.In this paper, the characteristics, genesis, significance to Pb-Zn mineralization of the widely developed breccias, and the ore-forming process have been carefully studied based on geological documentation of drilling holes, microscopic observations of petrography and microstructure and some stable isotope measurements.Based on the compositions of the clast and matrix, the breccias can be classified into three types: limestone clasts cemented by marl; limestone clasts with fine-grained calcareous materials; and limestone clasts cemented by hydrothermal calcite.The mineralization in the first type of breccia is weak, whereas it is strong in the latter two types of breccias.According to the locations of occurrence and structural characteristics of the breccias along with the relationship between the breccias and mineralization, part of the limestone clasts that are cemented by marl and outcrop in the contact zone between the Wudaoliang Formation(Nw) and the underlying Jiushidaoban Formation(Pj) are attributed to synsedimentary fault-genetic breccia, whereas the last of the limestone clasts that are cemented by marl and developed in the Jiushidaoban Formation(Pj) are attributed to the breccia generated by karst cave collapse; the limestone clasts with fine-grained calcareous materials and the limestone clasts cemented by hydrothermal calcite are attributed to breccia formed by hydrothermal dissolution.The breccia formed by karst collapse had consistently evolved for a long period of time, while the breccias with other origins were formed around the period of mineralization(i.e., about or slightly later than 20–16 Ma).The breccia generated by karst cave collapse and hydrothermal dissolution are somewhat related; the formation of the breccia from karst cave collapse provided open space for the later mineralization and reaction between hydrothermal fluids and host rocks, and the subsequent strong dissolution by hydrothermal fluids transformed some of the breccia formed earlier by karst cave collapse.Meanwhile, carbonate host rocks with breccias and brecciaed mineralization can be a potential sign of Mississippi Valley Type(MVT) deposits and important indicators for regional mineral exploration.The δ13CV-PDB, δ18OVSMOW, and 87Sr/86 Sr values of hydrothermal calcite in the Duocaima deposit range from 4.3‰ to 7.1‰, 14.9‰ to 20.1‰, and 0.707494 to 0.708185, respectively; the δ13CV-PDB, δ18OV-SMOW, and 87Sr/86 Sr values of the host limestones of the Jiushidaoban Formation range from 3.6‰ to 5.3‰, 18.0‰ to 20.5‰, and 0.707372 to 0.707945, respectively.The δ13CV-PDB and 87Sr/86 Sr values of hydrothermal calcite and limestone are similar, indicating single sources of C and Sr in this deposit, with the likely source being the limestone of the Jiushidaoban Formation.The minor scattering of the δ18OV-SMOW values suggests that different O isotope fluids underwent the isotope exchange reaction.The C-O-Sr isotope characteristics indicate that the host limestones experienced a dissolution and precipitation process during mineralization, which is beneficial to improving the porosity of host rocks and promoting the precipitation of metal sulfides.The δ34SV-CDT value of the breccia-type mineralization sulfides ranges from-30.4‰ to-0.3‰; that is, the δ34SV-CDT value is negative with considerable variation, illustrating that during the breccia-type mineralization process, the bacteriogenic reduction of sulfates provided the vast majority of sulfur, whereas the thermochemical reduction of sulfates was relatively unimportant.The brecciation that occurred as a result of karst cave collapse was mainly generated by the dissolution of groundwater; however, the brecciation related to hydrothermal dissolution and mineralization processes were caused by mixing of different fluids.     

祁连山中段托勒山地区奥陶纪火山岩岩金矿床控矿因素分析

[摘 要] 祁连山中段托勒山岩金多分布在奥陶纪火山岩地层内,地层控矿特征十分明显。区内与火山活动有关的成矿作用主要是火山喷发后期火山热液形成的热液型矿床,其次是后期岩浆活动提供热源和大量的岩浆热液交代、充填形成中低温热液矿床和接触蚀变型矿床。从找矿前景上来看,本区虽然金矿点、矿化点分布较多,但少有规模较大的矿床。因此本区找矿上应该以寻找火山热液蚀变型矿产为主。     

赣北大湖塘矿集区超大型钨矿地质特征及成因探讨

江西北部大湖塘地区发现世界级超大型钨矿床,使赣北成为继赣南之后我国又一重要的钨成矿省。大湖塘矿集区包括北区、南区和大雾塘矿区,正在开采的矿床有北区的石门寺矿床(己探明WO3金属量为74.255×104t)和南区的狮尾洞矿床(己探明WO3金属量31.09×104t),正在找矿勘查的矿区有北区的大岭上、大雾塘矿区平苗、东陡崖、一矿带等。矿化类型有细脉浸染型、石英大脉型、蚀变花岗岩型、云英岩型及隐爆角砾岩型钨(铜、钼)矿等多种类型,黑钨矿与白钨矿矿体共存、钨铜共生是该矿区成矿的显著特征。区内出露的沉积地层为新元古代双桥山群浅变质岩,岩浆岩为晋宁期的黑云母花岗闪长岩和燕山期多种岩性的花岗岩。燕山期主要有两期,早期为斑状花岗岩,成岩年龄约144Ma,如狮尾洞矿床的似斑状白云母(二云母)花岗岩、石门寺矿床的斑状黑云母花岗岩等,晚期为狮尾洞和大岭上矿床产出的中细粒花岗岩或花岗斑岩,成岩年龄约135~130Ma。这些岩浆的源区很可能来源于双桥山群的泥质变质沉积岩。富钨铜等成矿元素的双桥山群泥质变质岩部分熔融可初步形成含矿花岗岩浆,岩浆在高度结晶分异过程中则可使得钨铜等金属进一步富集在岩浆热液中,通过两期岩浆与成矿作用,最终形成超大型的大湖塘钨矿床。     

Geology, Mineralogy, and Formation Environment of the Disseminated Gold-Silver Telluride Bulawan Deposit, Negros Occidental, Philippines

Abstract: The Bulawan deposit is located in the porphyry copper belt of southwest Negros island, Philippines. Propylitic, K–feldspar, sericitic, and carbonate alteration types can be distinguished in the deposit. Propylite alteration occurs mainly in Cretaceous-Eocene andesitic lavas and agglomerates while K–feldspar, sericite and carbonate alteration types occur mostly in the Middle Miocene dacite porphyry breccia pipes and stocks which were intruded into the andesites. K-feldspar zones occur in the inner parts of the sericitized zone. Sericite alteration overprinted the propylitized and K-feldspar alteration zones, at lower temperature than epidote and chlorite in the propylitized zone. Carbonate alteration is associated with the mineralization in the center of the breccia pipes and along faults. Mineralization consists of gold-silver telluride ores that are hosted by the carbonate– and sericite-altered dacite porphyry breccia pipes. The Bulawan ores occur mainly as disseminations, but unlike many epithermal gold deposits, lack classical epithermal colloform and crustiform quartz veins. The ore minerals are sphalerite, galena, chalcopyrite, pyrite and tetrahedite-tennantite with minor amounts of electrum, calaverite, petzite, sylvanite, hessite, tellurobismuthite, coloradoite, altaite, and rucklidgeite. Electrum and telluride minerals are associated mostly with calcite and dolomite-ankerite minerals. Fluid inclusions in quartz and calcite in clasts of propylitized andesite in the breccia pipes homogenize from about 300° to 400°C while fluid inclusions in quartz, calcite and sphalerite within the dacite porphyry breccia pipes homogenize between 300° to 310°C. The ores were formed around 300°C from hydrothermal solutions with salinity of about 6. 6 wt % NaCl equivalent. The presence of sylvanite and calaverite as intergrowths with each other, and the Ag content of calaverite are consistent with the above temperature estimate. Based on paragenesis, the Bulawan deposit formed in a pyrite-stable environment, with pH between 3. 4 and 5. 5, f_O2 between 10^-32 to 10^-30 atm, f_S2 between 10^-9.8 to 10^-7.8 atm, f_Te2 between 10^-8.9 to 10^-6.5 atm, and total sulfur content about 10^-2.8 molal. The dominant reduced sulfur species in the ore solutions may have been H₂S_(aq), and the likely aqueous tellurium species were H₂Te_(aq) and H₂TeO_3(aq). The ore minerals in the Bulawan deposit were probably formed by mixing of slightly saline and low salinity fluids.     

The transition from porphyry- to epithermal-style gold mineralization at Ladolam, Lihir Island, Papua New Guinea: a reconnaissance study

The exceptionally large gold resource at Ladolam (>1,300 metric tons of gold), Lihir Island, resulted from the transition of an early-stage, low-grade porphyry gold system to a low-sulfidation epithermal gold event. This transition was probably triggered by rapid decompression during the partial slope failure of Luise stratovolcano and accompanied by the ingress of seawater. The original porphyry stage is indicated by remnant hydrothermal breccia clasts of strongly biotite-magnetite altered monzodiorite with disseminated pyrite - chalcopyrite and poorly developed pyrite - quartz stockwork veins. The breccias are overprinted by biotite-magnetite alteration and their matrix is strongly mineralized with disseminated auriferous pyrite. The breccias are cut by late-stage epithermal quartz-chalcedony-illite-adularia-pyrite veins and associated illite-adularia alteration that locally contain bonanza gold grades of up to 120 g/t. Isotope data suggest a magmatic source of sulfur in the gold-bearing fluids at Ladolam. Electronic supplementary material to this paper can be obtained by using the Springer LINK server located at http://dx.doi.org/10.1007/s00126-001-0230-y     

Adakite-like signature of Late Miocene intrusions at the Los Pelambres giant porphyry copper deposit in the Andes of central Chile: metallogenic implications

Adakite-like features are recognized in the Late Miocene (~10 Ma) porphyritic intrusions of the Los Pelambres giant porphyry copper deposit, central Chile (32°S). Located within the southern portion of the flat-slab segment (28–33°S) of the Chilean Andes, the Al- and Na-rich porphyries of Los Pelambres display distinctly higher Sr/Y (~100–300) and La_N/Yb_N (~25–60) ratios than contemporaneous and barren magmatic units (e.g., La Gloria pluton, Cerro Aconcagua volcanic rocks) of the same Andean magmatic belt. Strong fractionation of heavy rare earth elements (HREE), absence of Eu anomalies, high Sr/Y and Zr/Sm and low Nb/Ta ratios suggest melt extraction from a garnet-amphibolite source. The Late-Miocene adakite-like porphyritic intrusions at Los Pelambres formed closely related in time and space to the subduction of the Juan Fernández Ridge (JFR) hotspot chain along the Chilean margin. Current tectonic reconstructions reveal that, at the time of formation of the Los Pelambres rocks, a W-E segment of the JFR started to subduct beneath them, producing a slow-down of a previously rapid southward migration of a NE-ridge—trench collision. These particular tectonic conditions are favorable for the origin of the Los Pelambres porphyry suite by melting of subducting young hotspot rocks under flat-slab conditions. The incorporation of crustal components into the oceanic lithopheric magma source by subduction erosion is evidenced by the Sr-Nd isotope composition of the Los Pelambres rocks different from the MORB signatures of true adakites. A close relationship apparently exists between the origin of this adakite-like magmatism and the source of the mineralization in the Los Pelambres porphyry copper deposit.Editorial handling: R.J. Goldfarb     

Formation of albitite-hosted uranium within IOCG systems: the Southern Breccia,Great Bear magmatic zone,Northwest Territories,Canada

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.     

伊朗浅成低温热液矿床时空分布规律与矿床类型

特提斯成矿域是地球上三大成矿域之一,矿产资源丰富.文章综述了特提斯域内伊朗高原浅成低温热液矿床的地质特征,讨论了成矿事件的时空分布规律以及主要矿床类型.研究表明,伊朗浅成低温热液矿床大部分位于乌兹密尔-杜克塔尔岩浆弧和阿尔博兹岩浆弧.其中,前者主要产出高硫型Cu-Au±Ag矿床和低硫型Au±Ag±Cu矿床,分布较为稀疏...