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Jens Gutzmer 《Mineralium Deposita》2006,40(6-7):664-685
The Pering deposit on the Ghaap Plateau, Northwestern Province, South Africa, was the largest of several Zn–Pb occurrences hosted by Neoarchean platform dolostones of the Transvaal Supergroup. With a Paleoproterozoic mineralization age, these occurrences are widely regarded as the oldest representatives of Mississippi Valley-type Pb–Zn deposits. Hosting an initial resource of 18 Mt at an average grade of 3.6 wt% Zn and 0.6 wt% Pb, the Pering deposit was mined from 1984 until its final closure at the end of November 2002. In this study, available geological and grade distribution maps were evaluated and complemented by the examination of mining-related outcrops, drill core, and a large set of ore and host rock samples. Four different styles of brecciation can be distinguished at the Pering deposit: (1) pyritic rock matrix breccia; (2) chemical wear breccia; (3) mosaic breccia; and (4) crackle breccia. Geological and mineral paragenetic observations on these different breccia types suggest that the formation of the Pering deposit commenced with an initial stage of hydrothermal karstification. Large volumes of pyritic rock matrix breccia formed by wall rock collapsing into the open space attributed to carbonate dissolution. This stage of hydrothermal karstification acted as ground preparation for the subsequent mineralization event. By the upward advance of the hydrothermal karstification process, fluid reservoirs in the previously undisturbed dolostone host rock succession were tapped, ultimately leading to fluid mixing. Hydrothermal sulphides are the most abundant where fluid mixing was most effective, i.e. along the outer and upper margins of the breccia bodies, and in stratabound zones along permeable host rock units. Chemical wear brecciation and formation of large volumes of fine-grained replacive sphalerite mineralization mark the early stage of hydrothermal Zn–Pb mineralization associated with this fluid mixing. The fine-grained stage of sulphide mineralization was succeeded by very coarse-grained open-space-infill mineralization. The latter is very uniform across the entire deposit and typically cements mosaic and crackle breccia, but also fills remaining open space within chemical wear brecciated portions of the deposit. 相似文献
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湖南省热液硅化成矿作用与找矿 总被引：2，自引：0，他引：2
根据成矿作用与热液硅化极为密切的锡矿山锑矿床、康家湾铅锌金矿床、磺厂雄磺矿床和320铀矿床的地质特征,对热液硅化、角砾化、矿质沉淀和矿床剖面结构的形成机理进行了讨论,认为这类矿床属于浅成热液类型矿床或热泉型矿床,进而认为对司空见惯的硅化带的找矿意义要重新认识,由此提出了寻找这种类型矿床的地质、地球化学、地球物理的找矿标志。 相似文献
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Nadia Vogel Heinrich Baur Addi Bischoff Rainer Wieler 《Chemie der Erde / Geochemistry》2011,(2):135-142
We analyzed noble gases and determined 3He, 21Ne, and 38Ar cosmic ray exposure ages (CREAs) of Rumuruti chondrites from North West Africa (NWA) to rule on potential pairings and/or source pairings of North Africa R chondrite samples. The 21Ne exposure ages range between 10 and 74 Ma, with NWA 2897 and 1668 having the highest known exposure ages among R chondrites. We also include other R chondrites from North Africa (Schultz et al., 2005) and, based on their noble gas characteristics and their 21Ne CREAs, propose pairings of the following samples: NWA 2198, 5069, 755, 4615, 845, 851, 978, 1471, and possibly DaG 013 belonging to one fall with a CREA of ∼10 Ma, and NWA 753, 4360, 4419, 5606, 1472, 1476, 1477, 1478, and 1566 representing one fall with a CREA of ∼14 Ma. NWA 2821, 2503, 2289, 3364, 3146, 4619, 4392, 3098, and 2446 seem to belong to one single fall with a CREA of ∼20 Ma, and NWA 2897 and 1668 seem to be paired and show a common CREA of ∼66 Ma. Overall, all R chondrite samples from North Africa analyzed for noble gases so far represent ∼16 individual falls. Comparing falls from North Africa to literature CREAs of R chondrites worldwide, it seems possible that a significant number of all R chondrite falls studied for noble gases were ejected from the R chondrite parent body during one large collisional event between 15 and 25 Ma ago. However, the database is still too small to draw definitive conclusions. The large portion of brecciated R chondrites in collections suggests severe impact brecciation of the R chondrite parent body. 相似文献
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In the uppermost Jurassic of the central part of the South-East Basin of France, an association of lime mudstone beds, calcarenite beds and coarse carbonate breccia bodies form an informal stratigraphical unit called the 'Barre Tithonique'. In the 'Barre Tithonique', gradual transitions from lime mudstone or calcarenite to breccia show different stages of deformation leading to progressive brecciation of the original lithologies. The study of the breccia facies, and the observed gradual transitions as a whole, document a new early diagenetic process in carbonate environments, resulting from water-wave and seabed interaction. Water-wave induced brecciation and its abundance in the 'Barre Tithonique' indicate that sea–seabed interaction was significant. Comparison with modern studies of the mechanics of wave–seabed interaction suggests that water depth was less than 200 m. It is demonstrated that sedimentary features such as channel-like structures, previously interpreted as being the result of erosion and deposition of mud-flows, were in fact produced by wave-induced, in situ reworking of lime mud, without any significant unidirectional flow or gravity induced displacement. 相似文献
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Numerical modelling of deformation and fluid flow in the Shuikoushan district, Hunan Province, South China 总被引：3，自引：2，他引：3
The Shuikoushan district, in Hunan Province, South China, contains major Pb–Zn–Au–Ag polymetallic mineralisation. Two groups of numerical models have been constructed to study the interactions between deformation and fluid flow in the district during the Yanshanian compression event (180 to 90 Ma). The first group includes district-scale conceptual models of coupled deformation and fluid flow during folding. The models show that fluid flow patterns are controlled by deformation within the fold system inferred for the district. During regional shortening and folding, fluids are generally focused towards the fold hinge/core areas along higher permeability layers (in particular Permian limestone units), in preference to flowing across the low permeability seal units (Permian and Jurassic terrestrial sequences). The efficiency of this fluid focusing can only be significantly increased if these folded seal units are allowed to undergo permeability increase as a result of tensile failure. The modelling results show that permeability enhancement localises mostly at fold hinges, dominantly within the silicified zone on the top of the Permian limestone unit. This process results in increased flow velocities and facilitates fluid focusing towards fold hinge/core locations at this silicified rock horizon. The second group includes deposit scale models for the Kangjiawan deposit, which is one of the two major deposits in the Shuikoushan district. The models show patterns of tensile failure, permeability creation, fluid focusing and mixing, and fracture development along a selected exploration cross section through the deposit. These results are consistent with the observed brecciation and mineralisation features. Regions of maximum brecciation in the district are associated with: (1) a combination of fold hinge and fault intersection locations (structural); and (2) the silicified zone and Permian limestone unit (lithological). Such brecciation zones are associated with extensive fluid focusing and mixing, and therefore represent the most favourable locations for mineralisation in the district. On the basis of this work, ideas for future research work and mineral exploration in the district are proposed. 相似文献
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《Chemie der Erde / Geochemistry》2019,79(4):125518
The main mineralogical characteristics of a large light-colored clast within the Murchison CM breccia are discussed in detail including data on the mineralogy, bulk chemistry, organics, and oxygen isotopes. Petrographic study shows that the white clast consists of two areas with different granoblastic textures: (1) a coarse-grained (average grain size: ∼200 μm) and (2) a fine-grained lithology (average grain-size: ∼20 μm). The Fa-content of olivine in the clast is the same as Fa within olivine from Rumuruti (R) chondrites (Fa: ∼38 mol%); however, the concentrations of the elements Ni and Ca in olivine are significantly different. The fragment also contains Ca-rich pyroxene, ∼An30-38-plagioclase/maskelynite, Cr-rich spinel, several sulfide phases, a nepheline-normative glass, and traces of merrillite and metal. The occurrence of maskelynite and nepheline-normative amorphous phase in restricted areas of the well-recrystallized rock may indicate remarkable P-T-excursions during shock metamorphism. The O-isotope composition of the clast falls below the terrestrial fractionation line (TFL), lying in the field of CM chondrites and is significantly different from data for bulk R chondrites. The study of the soluble organic matter revealed a highly-oxidized carbon chemistry and organomagnesium compounds reflecting high temperature and pressure processes. 相似文献
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