巴西与碱性岩- 碳酸岩杂岩体相关的关键矿产成矿作用与规律

在巴西,与碱性岩- 碳酸岩杂岩体相关成矿作用复杂,产出了世界上唯一的霞石正长岩型斜锆石矿床、全球最大的铌矿床以及巴西最大的铀矿和镍矿集区,资源储量丰富,具有重要的经济价值和战略意义,同时也是关键矿产成矿作用研究的殿堂。本文在前人研究基础之上,整理分析了35处与碱性岩- 碳酸岩相关的关键矿产地质特征。根据成矿作用特征,划分了4个成矿系列:①霞石正长岩碱性杂岩相关的U- Zr- Mo- REE 和萤石成矿系列;②碱性岩- 碳酸岩杂岩(正长岩+辉石岩+霓霞岩+碳酸岩等)相关的Nb- P- Ti- REE和蛭石成矿系列;③阿拉斯加型超基性岩- 碱性杂岩体相关的Ni成矿系列;④交代正长岩相关的U- P成矿系列。根据关键矿产资源时空分布规律,划分了5个成矿带:(Ⅰ)Lancinha- Cubato碱性岩- 碳酸岩相关REE- P- U- Zr- Ni- Mo- 蛭石成矿带;(Ⅱ)Rio de Janeiro- Rondnia碱性岩- 碳酸岩- 金伯利岩相关的Nb- REE- Ti- Zr- P- 金刚石成矿带;(Ⅲ)Ceará- Mato Grossodo Sul 超基性岩- 碱性岩- 碳酸岩相关的Ni- U- P- 蛭石成矿带;(Ⅳ)亚马逊地区碳酸岩相关Nb- REE- Th- Ti- P成矿带;(Ⅴ)巴伊亚地区与变正长岩相关的U成矿带。本文还详细介绍了典型矿床成矿地质特征和成矿条件,为走出去寻找关键矿产资源基地提供了理论支撑。     

Topical problems of gold metallogeny

Siberian geologists in general and Academician V.A. Kuznetsov in particular made a considerable contribution to metallogeny. To follow them, we consider regularities of location and formation of gold deposits. Analysis of topical problems of gold metallogeny reflects general problems of state-of-the-art metallogeny. The analysis is based on concepts of geologic-genetic types of gold deposits and metallogenic specialization of geodynamic-geotectonic regimes and settings. The types of endogenic-polygenic gold ore and gold-bearing deposits restricted to certain settings — among which, in addition to traditional ones, intracratonic basins have been established — are characterized by depressions and heterochronous areas of rift and plume tectonomagmatic activity.     

The time-space distribution of Eocene to Miocene magmatism in the central Peruvian polymetallic province and its metallogenetic implications

Eocene to late Miocene magmatism in the central Peruvian high-plain (approx. between Cerro de Pasco and Huancayo; Lats. 10.2–12°S) and east of the Cordillera Occidental is represented by scattered shallow-level intrusions as well as subaerial domes and volcanic deposits. These igneous rocks are calc-alkalic and range from basalt to rhyolite in composition, and many of them are spatially, temporally and, by inference, genetically associated with varied styles of major polymetallic mineralization. Forty-four new ⁴⁰Ar–³⁹Ar and three U/Pb zircon dates are presented, many for previously undated intrusions. Our new time constraints together with data from the literature now cover most of the Cenozoic igneous rocks of this Andean segment and provide foundation for geodynamic and metallogenetic research.The oldest Cenozoic bodies are of Eocene age and include dacitic domes to the west of Cerro de Pasco with ages ranging from 38.5 to 33.5 Ma. South of the Domo de Yauli structural dome, Eocene igneous rocks occur some 15 km east of the Cordillera Occidental and include a 39.34 ± 0.28 Ma granodioritic intrusion and a 40.14 ± 0.61 Ma rhyolite sill, whereas several diorite stocks were emplaced between 36 and 33 Ma. Eocene mineralization is restricted to the Quicay high-sulfidation epithermal deposit some 10 km to the west of Cerro de Pasco.Igneous activity in the earliest Oligocene was concentrated up to 70 km east of the Cordillera Occidental and is represented by a number of granodioritic intrusions in the Milpo–Atacocha area. Relatively voluminous early Oligocene dacitic to andesitic volcanism gave rise to the Astabamba Formation to the southeast of Domo de Yauli. Some stocks at Milpo and Atacocha generated important Zn–Pb (–Ag) skarn mineralization. After about 29.3 Ma, magmatism ceased throughout the study region. Late Oligocene igneous activity was restricted to andesitic and dacitic volcanic deposits and intrusions around Uchucchacua (approx. 25 Ma) and felsic rocks west of Tarma (21–20 Ma). A relationship between the Oligocene intrusions and polymetallic mineralization at Uchucchacua is possible, but evidence remains inconclusive.Widespread magmatism resumed in the middle Miocene and includes large igneous complexes in the Cordillera Occidental to the south of Domo de Yauli, and smaller scattered intrusive centers to the north thereof. Ore deposits of modest size are widely associated with middle Miocene intrusions along the Cordillera Occidental, north of Domo de Yauli. However, small volcanic centers were also active up to 50 km east of the continental divide and include dacitic dikes and domes, spatially associated with major base and precious metal mineralization at Cerro de Pasco and Colquijirca. Basaltic volcanism (14.54 ± 0.49 Ma) is locally observed in the back-arc domain south of Domo de Yauli approximately 30 km east of the Cordillera Occidental.After about 10 Ma intrusive activity decreased throughout Central Perú and ceased between 6 and 5 Ma. Late Miocene magmatism was locally related to important mineralization including San Cristobal (Domo de Yauli), Huarón and Yauricocha.Overall, there is no evidence for a systematic eastward migration of the magmatic arc through time. The arc broadened in the late Eocene to early Oligocene, and thereafter ceased over wide areas until the early Miocene, when magmatism resumed in a narrow arc. A renewed widening and subsequent cessation of the arc occurred in the late middle and late Miocene. The pattern of magmatism probably reflects two cycles of flattening of the subduction in the Oligocene and late Miocene. Contrasting crustal architecture between areas south and north of Domo de Yauli probably account for the differences in the temporal and aerial distribution of magmatism in these areas.Ore deposits are most abundant between Domo de Yauli and Cerro de Pasco and were generally emplaced in the middle and late Miocene during the transition to flat subduction and prior to cessation of the arc. Eocene to early Oligocene mineralization also occurred, but was restricted to a broad east–west corridor from Uchucchacua to Milpo–Atacocha, indicating a major upper-plate metallogenetic control.     

Geodynamics and metallogeny of the central Eurasian porphyry and related epithermal mineral systems: A review

Major porphyry Cu–Au and Cu–Mo deposits are distributed across almost 5000 km across central Eurasia, from the Urals Mountains in Russia in the west, to Inner Mongolia in north-eastern China. These deposits were formed during multiple magmatic episodes from the Ordovician to the Jurassic. They are associated with magmatic arcs within the extensive subduction–accretion complex of the Altaid and Transbaikal-Mongolian orogenic collages that developed from the late Neoproterozoic, through the Palaeozoic, to the Jurassic intracratonic extension. The arcs formed predominantly on the Palaeo-Tethys Ocean margin of the proto-Asian continent, but also within two back-arc basins. The development of the collages commenced when slivers of an older Proterozoic subduction complex were rifted from an existing cratonic mass and accreted to the Palaeo-Tethys Ocean margin of the combined Eastern Europe and Siberian cratons. Subduction of the Palaeo-Tethys Ocean beneath the Karakum and Altai-Tarim microcontinents and the associated back-arc basin produced the overlapping late Neoproterozoic to early Palaeozoic Tuva-Mongol and Kipchak magmatic arcs. Contemporaneous intra-oceanic subduction within the back-arc basin from the Late Ordovician produced the parallel Urals-Zharma magmatic arc, and separated the main Khanty-Mansi back-arc basin from the inboard Sakmara marginal sea. By the Late Devonian, the Tuva-Mongol and Kipchak arcs had amalgamated to form the Kazakh-Mongol arc. By the mid Palaeozoic, the two principal cratonic elements, the Siberian and Eastern European cratons, had begun to rotate relative to each other, “drawing-in” the two sets of parallel arcs to form the Kazakh Orocline between the two cratons. During the Late Devonian to Early Carboniferous, the Palaeo-Pacific Ocean began subducting below the Siberian craton to form the Sayan-Transbaikal arc, which expanded by the Permian to become the Selanga-Gobi-Khanka arc. By the Middle to Late Permian, as the Kazakh Orocline continued to develop, both the Sakmara and Khanty-Mansi back-arc basins were closed and the collage of cratons and arcs were sutured by accretionary complexes. During the Permian and Triassic, the North China craton approached and docked with the continent, closing the Mongol-Okhotsk Sea, an embayment on the Palaeo-Pacific margin, to form the Mongolian Orocline. Subduction and arc-building activity on the Palaeo-Pacific Ocean margin continued to the mid Mesozoic as the Indosinian and Yanshanian orogens.Significant porphyry Cu–Au/Mo and Au–Cu deposits were formed during the Ordovician in the Kipchak arc (e.g., Bozshakol Cu–Au in Kazakhstan and Taldy Bulak porphyry Cu–Au in Kyrgyzstan); Silurian to Devonian in the Kazakh-Mongol arc (e.g., Nurkazgan Cu–Au in Kazakhstan and Taldy Bulak-Levoberezhny Au in Kyrgyzstan); Devonian in the Urals-Zharma arc (e.g., Yubileinoe Au–Cu in Russia); Devonian in the Kazakh-Mongol arc (e.g., Oyu Tolgoi Cu–Au, and Tsagaan Suvarga Cu–Au, in Mongolia); Carboniferous in the Kazakh-Mongol arc (e.g., Kharmagtai Au–Cu in Mongolia, Tuwu-Yandong Cu–Au in Xinjiang, China, Koksai Cu–Au, Kounrad Cu–Au and the Aktogai Group of Cu–Au deposits, in Kazakhstan); Carboniferous in the Valerianov-Beltau-Kurama arc (e.g., Kal’makyr–Dalnee Cu–Au in Uzbekistan; Benqala Cu–Au in Kazakhstan); Late Carboniferous to Permian in the Selanga-Gobi-Khanka arc (e.g., Duobaoshan Cu–Au in Inner Mongolia, China); Triassic in the Selanga-Gobi-Khanka arc; and Jurassic in the Selanga-Gobi-Khanka arc (e.g., Wunugetushan Cu–Mo and Jiguanshan Mo in Inner Mongolia, China). In addition to the tectonic, geologic and metallogenic setting and distribution of porphyry Cu–Au/Mo mineralisation within central Eurasia, the setting, geology, alteration and mineralisation at each of the deposits listed above is described and summarised in Table 1.