The South Faizuly manganese deposit in the southern Urals: Geology,petrography, and formation conditions

The South Faizuly manganese deposit hosted in cherty rocks of the Magnitogorsk paleovolcanic belt has been studied. The geology, mineralogy, and chemistry of ores and host silicites (jasperites, jaspers, and cherty siltstones) are characterized. The deposit was formed in the following four consecutive stages: (1) sedimentation and diagenesis of ore-bearing sediments in the Middle Devonian, (2) metagenesis of Mn-bearing rocks in the Middle Devonian-Early Carboniferous, (3) hydrothermal-metasomatic stringer ore mineralization during tectonic deformation of volcanosedimentary rocks in the Middle Carboniferous-Permian, and (4) supergene alteration and partial denudation of the deposit in the Mesozoic-Quaternary. Models of Mn-bearing rock deposition in the proximal and distal zones of the hydrothermal solution discharge area are considered.Translated from Litologiya i Poleznye Iskopaemye, No. 1, 2005, pp. 35–55.Original Russian Text Copyright 2005 by Brusnitsyn, Zhukov.     

The Vorontsovskoe Au-Hg-As ore deposit (Northern Urals,Russia): Geological setting,ore mineralogy,geochemistry, geochronology and genetic model

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.     

Geochemistry and formation model of manganiferous rocks in jaspers of the South Urals

Specific features of the geochemistry of manganiferous siliceous rocks confined to Devonian volcanogenic complexes of the Magnitogorsk belt in the South Urals are discussed. It is shown that with respect to the distribution of the major petrogenic and rare earth elements, as well as base and rare metals, manganese rocks are comparable with rocks of the low-temperature hydrothermal sources in active volcanic zones of the World Ocean. Our results agree well with the existing concepts about the hydrothermal-sedimentary origin of manganese deposits in the South Urals and corroborate this hypothesis with new independently obtained data.     

Mineralogy and metamorphism conditions of manganese ore at the South Faizulino deposit, the southern Urals, Russia

The mineralogy of slightly metamorphosed manganese ore at the South Faizulino hydrothermalsedimentary deposit in the southern Urals has been studied; 32 minerals were identified. Quartz, hausmannite, rhodochrosite, tephroite, ribbeite, pyroxmangite, and caryopilite are major minerals; calcite, kutnahorite, alleghanyite, spessartine, rhodonite, clinochlore, and parsettensite are second in abundance. This mineralic composition was formed in the process of gradual burial of ore beneath the sequence of Middle Devonian-Lower Carboniferous rocks. The highest parameters of metamorphism are T ≈ 250°C and P ≈ 2.5 kbar. The relationships between minerals and their assemblages made it possible to reconstruct the succession of ore transformation with gradually increasing temperature and pressure. Manganese accumulated in the initial sediments as oxides and a gel-like Mn-Si phase. Rhodochrosite and neotocite were formed at the diagenetic stage. In the course of a further increase in temperature and pressure, neotocite was replaced with caryopilite; ribbeite, tephroite, pyroxmangite, and other silicates crystallized afterwards. In addition to the PT parameters, the formation of various metamorphic mineral assemblages was controlled by the Mn/(Mn + Si) ratio in ore and X _CO2 in pore solution. The latter parameter was determined by the occurrence of organic matter in the ore-bearing rocks. Ore veinlets as products of local hydrothermal redistribution of Mn, Si, and CO₂ were formed during tectonic deformations in the Middle Carboniferous and Permian.     

Manganese metalliferous sediments of the Deryugin Basin (Sea of Okhotsk): Chemical composition and geological setting

This paper reports the results of an investigation of the chemical composition and distribution of manganese-rich metalliferous sediments in the Deryugin Basin. They compose an upper sedimentary layer up to 30 cm thick within a strip up to 40 km wide and 180 km long in the central part of the basin along the East Deryugin suture zone bounding the Deryugin sedimentary basin to the east. The sediments are enriched relative to the regional background composition in Mn (by a factor of 35); Au; Ni; Zn; Co (by a factor of 3–5); and, locally, in Mo, V, Ba, Cu, Pb, and Hg. It was supposed that their formation was controlled by several processes: precipitation of Mn and some other trace elements from hydrothermal plumes of seawater that occasionally form above submarine hot vents in the northern part of the basin, precipitation from anoxic bottom waters at the eastern boundary of the Deryugin sedimentary basin, and early diagenetic migration of Mn into the surface sediments.     

The Pokrovskoe gold-silver deposit (Amur Region): Geological settings, formation factors, and ore mineralogy

The Pokrovskoe gold-silver deposit is explored by drill holes. Its gently dipping orebodies (lodes) revealed by core sampling are quarry mined. It is considered that they also consist of gently dipping quartz veins and vein-stringer zones. The performed investigation of the terraces in the exploited quarries made it possible to correct the available present-day concepts. It is shown that their structure is dominated by steeply dipping veins and vein-stringer zones. They are characterized by the northeastern strike in the central part of the deposit and its western flank and the mostly northwestern one in its eastern part. An important role in the formation and distribution of the orebodies belongs to various geological screens poorly permeable for fluids. The main factors responsible for the ore localization in screened hydrogeological systems are revealed with the assessment of the thermal impact of a dacite sill on the formation of the ore-hosting cavities and ore deposition. The electron microscope investigation of the ores substantially widened the spectrum of ore minerals previously unknown in this deposit, including gold-bearing varieties (copper gold and its complex intermetallic compounds). Based on the dominant micrometer sizes of all the ore minerals and their dispersion within the quartz matrix, it is inferred that the deposition of productive ores occurred in nonequilibrium environments.     

华南地区三叠纪矿床地质特征、成矿规律和矿床模型

华南以中生代成矿大爆发为特征,燕山期矿床成矿规律的研究程度较高,近年来发现越来越多的三叠纪矿床,但三叠纪矿床的分布规律和矿床模型是值得关注的重要科学问题。本文基于最新研究成果,论述华南三叠纪矿床地质特征和矿床类型,提出成矿规律,初步地建立成矿动力学模型。华南地区三叠纪矿床分布较为广泛,目前确定的46个三叠纪矿床分布于5个区带,形成于晚三叠世 (230~200 Ma),被划分为花岗岩有关的钨锡多金属矿床、侵入岩有关的远端金锑矿床、卡林型金矿床和MVT型铅锌矿床4种主要类型。在空间上,华南三叠纪矿床存在成矿元素分带性,由西向东依次为MVT型铅锌矿床、卡林型金矿床、侵入岩有关的远端金锑矿床、花岗岩有关的钨锡多金属矿床。华南5个成矿区带普遍存在印支期和燕山期的叠加成矿作用,在南岭西段桂北苗儿山—越城岭和滇东南老君山地区还发育加里东和印支期的叠加成矿作用。     

Geochemistry of Early Devonian rocks of the Sakmara zone,South Urals

This paper reports first isotope–geochemical data on the Early Devonian magmatic rocks of the Chanchar potassic mafic volcanoplutonic complex of the Sakmara zone of the South Urals. The incompatible element distribution and ratios indicate that the rocks of the volcanic, subvolcanic, and intrusive facies are comagmatic and were derived from a common source. The low HFSE concentrations relative to MORB and relatively low ⁸⁷Sr/⁸⁶Sr and high ¹⁴³Nd/¹⁴⁴Nd ratios suggest that primary melts were generated from a moderately depleted mantle. The LILE enrichment of the rocks indicates a flux of mantle fluid in the primary magma during its evolution.     

Geological setting of the Wassa gold deposit,SW Ghana

Including past production, current indicated and inferred resources, Wassa is a 5 Moz poly-deformed early-orogenic gold deposit located on the eastern flank of the Ashanti Belt, in southwest Ghana. It is hosted by metamorphosed volcanic, intrusive and sedimentary rocks of the Sefwi Group (ca. 2260–2160 Ma). Early mineralization has an Eoeburnean age (2164 ± 22 Ma, Re–Os on pyrite) and is characterized by quartz veins, by a carbonate alteration of the host rocks, and by deformed gold-bearing pyrite. Remobilization of this gold occurred during the late stages of the Eburnean Orogeny (~ 2.1 Ga) and is associated with quartz-carbonate veins with visible gold and euhedral pyrites.     

南非维特沃特斯兰德盆地绍斯迪普金矿床地质特征、成矿模式和找矿模型

对南非兰德砾岩型金矿床的研究成果进行总结,概括了绍斯迪普金矿床的区域地质背景、岩石地层划分,较为系统地分析了矿床的地质特征和矿床成因。 得出如下结论：①金的主要来源可能与太古宙含金花岗绿岩带有密切关系;②金矿体主要受太古宙文特斯多普砾岩地层和中兰德群中的Turffontein亚群埃尔斯伯格组砾岩地层控制;③金矿床可能经历了早期沉积成岩成矿阶段—后期改造富集多个（Klipriviersberg火山活动作用时期和与2050Ma布什维尔德杂岩体有关的变质作用高峰时期）阶段,为复合成因的层控改造型矿床。研究结果对该类矿床的深入研究和走出去的中国企业有重要的参考价值。     

南非维特沃特斯兰德盆地绍斯迪普金矿床地质特征、成矿模式和找矿模型

对南非兰德砾岩型金矿床的研究成果进行总结,概括了绍斯迪普金矿床的区域地质背景、岩石地层划分,较为系统地分析了矿床的地质特征和矿床成因。得出如下结论:1金的主要来源可能与太古宙含金花岗绿岩带有密切关系;2金矿体主要受太古宙文特斯多普砾岩地层和中兰德群中的Turffontein亚群埃尔斯伯格组砾岩地层控制;3金矿床可能经历了早期沉积成岩成矿阶段—后期改造富集多个(Klipriviersberg火山活动作用时期和与2050Ma布什维尔德杂岩体有关的变质作用高峰时期)阶段,为复合成因的层控改造型矿床。研究结果对该类矿床的深入研究和走出去的中国企业有重要的参考价值。     

重庆高燕锰矿床含锰碳酸盐岩稀土元素特征

重庆城口高燕锰矿属于大型碳酸盐锰矿床。文章在系统野外地质调查及样品采集基础上,结合前人研究工作,采用等离子质谱仪(ICP-MS)分析了高燕矿区师家沟、板相沟及750平硐样品的稀土元素含量。分析结果显示,其稀土元素总量范围49.79×10~(-6)~281.24×10~(-6),平均含量125.92×10~(-6);轻重稀土比值范围1.79~3.58,显示轻稀土元素富集,且轻稀土元素之间的分馏程度高于重稀土元素;w(La)/w(Ce)=0.36~0.93,δEu=1.13~2.96,呈现弱正铕异常;δCe=2.09~5.84,有强的正铈异常。认为含锰碳酸盐岩形成于强还原的碱性环境沉积过程中,且有热水参与,成岩成矿的温度小于250℃,锰富集阶段处于滨岸的高能环境中。CeS10在本区具有示矿作用。     

Microinclusions of ore minerals in gold from the Miass placer zone (South Urals): Evidence for source rocks

Microinclusions of ore minerals were found and studied in grains of native gold for characterization of the mineralogy of placer gold of the South Urals. One hundred ten unrounded and poorly rounded grains with a size of 1–2 mm from eight placer zones were studied. Microinclusions of ore minerals were detected in six placers of the Miass zone. The list of minerals includes sulfides, arsenides, Cu-bearing Au, and PGEs. All microinclusions show links to certain deposits of ore gold and chromite occurrences. It is suggested that the northern flanges of the Talovsky and Nurali massifs containing gold placers with PGEs require a search for PGE mineralization.

     

Lithochemical composition of sandstones of the Vendian Asha Group,South Urals

The mineralogical–petrographic and chemical study of sandstones of the Vendian Asha Group in the Bashkir anticlinorium, the western slope of the South Urals, showed that this large stratigraphic unit consists of sedimentary associations formed in different conditions: (1) Pre-Uryuk sediments (Tolparovo, Suirovo, and Bakeevo formations) accumulated during marine regression possibly in the course of significant glacioeustatic sea level fluctuations and formation of the foredeep of Timanides. (2) Sediments of the Uryuk Formation, including alluvial and several related sediments. Analysis of the Qm–F–Lt, Qt–F–L, and ln(Q/L + CE)–ln(Q/F) diagrams showed that they were derived from magmatic/plutonic rocks in the inner parts of the East European Craton. Based on the distribution of data points of psammites in the Qt/(F + R)–Qp/(F + R) diagram, they were accumulated in the semihumid/semiarid conditions. (3) Coastal, shallowmarine, and fluvial/proluvial (?) sediments of the Basa, Kukkarauk, and Zigan formations. They were formed by the erosion of provenances located supposedly east of the present-day Bashkir anticlinorium. The psammites of the Asha Group were analyzed using the sandstone formation model proposed models proposed in (Dickinson et al., 1985; Garzanti et al., 2007). The distribution of data points of psammites from three uppermost formations of the Asha Group in the Qm–F–Lt and Qt–F–L diagrams suggests that they were accumulated by the redeposition of erosion products of the so-called clastic wedges of recycled orogens (clasticwedge provenance) made up of the fluvial and turbidite complexes of the foreland, fore-arc, or residual oceanic basins.     

广西钦州那必锰矿地质特征及成因认识

研究认为,那必锰矿为次生淋滤及堆积型矿床,其产出特点为：矿体主要产于紫色含锰硅质岩段（D3l^3）中,并受破碎带及层间裂隙控制,似层状产出,沿倾斜方向,延伸一般不会超过35m.其富集规律为：铁、锰矿沉积关系密切,菱锰矿与褐铁矿共生,但在表生淋滤环境下两者往往分离,锰质淋移至深部,而铁质则富集于上部.因此,含锰褐铁矿矿体常产于锰矿体的上部,可成为锰矿找矿的一种地表直接标志.