Xiao-Hua Deng

Porphyry Cu ore deposits are the main source for the Cu, Au, and Mo on Earth. In the porphyry Cu deposit systems, amphibole differentiation is a crusial step in the derivation of fertile, mineralising magmas. However, not all magmas produced through this process will host a porphyry copper deposit. In this study, a suite of amphibole-rich lithologies and contemporary, barren intermediate-acid rocks from Jinzhai, China, are examined to address the reasons for the differences in magma’s mineralisation potential through the studies of whole-rock geochemistry, U–Pb geochronology and zircon trace element chemistry. The changes in whole-rock chemistry are featured by a calc-alkaline differentiation trend and decreased Sr/Y, Eu/Eu*, Dy/Yb ratios, which are interpreted to reflect an intra-crustal magmatic evolution by low-pressure fractionation of amphibole + plagioclase during the regional switch from a compressional to a more extensional setting. By comparing with the amphibole-rich lithologies spa-temporally linking to the porphyry Cu deposit, we show a finding that low-pressure amphibole differentiation is not benefit for porphyry Cu as its potential failure to enhance the oxidation state or water content of residual melt.

The Central Asian Orogenic Belt (CAOB) hosts a variety of hydrothermal mineralised systems that formed during the opening, development and closure of the Paleo-Asian Ocean. Mercury is an important ore-forming metal in hydrothermal systems. Mercury photoreactions on the surface of Earth produce negative and positive Δ199Hg signals in terrestrial and marine sediments, respectively. Here, we observe positive Δ199Hg values in 345 to 320 Ma porphyry Cu deposits (+0.15 ± 0.15 ‰, s.d.), and a 355 Ma volcanogenic massive sulfide Cu–Zn deposit (+0.16 ± 0.13 ‰, s.d.) in the CAOB, which reflect the recycling of marine sediments during oceanic subduction and circulation of seawater in an extensional tectonic regime, respectively. In contrast, we observe negative Δ199Hg values in 232 to 227 Ma porphyry Mo deposits (−0.01 ± 0.07 ‰, s.d.) and a 245 Ma skarn W deposit (−0.02 ± 0.08 ‰, s.d.), which reflect the mixing of recycled Hg from marine and terrestrial sediments during continental collision. This study is useful in understanding the metallogenic effects of the Wilson Cycle and highlights that plate tectonics can cause intensive mobilisation, migration and mineralisation of Hg from subducted oceanic and continental crust to form Hg-bearing hydrothermal systems in long lived accretionary orogens.

The Yu'erya gold deposit is a large‐scale gold deposit in eastern Hebei. However, the ore genesis is controversial because the gold orebody is closely related to biotite granite in time and space. The hydrothermal processes of the Yu'erya gold deposit can be divided into early quartz (Q1)‐pyrite stage, middle quartz (Q2)‐sulphide stage and late quartz (Q3)‐calcite stage. The Q1 is subdivided into Q1‐1 and Q1‐2 generations by SEM‐CL images, and Q2 is subdivided into Q2‐1 and Q2‐2 generations. Three types of fluid inclusions (FIs), including aqueous‐carbonic type (C‐type), aqueous‐rich type (W‐type) and vapour‐rich type (V‐type), were observed in the Yu'erya gold deposit. The Q1‐1 is dominated by C‐type inclusions, and the other quartz is dominated by W‐type inclusions. Laser Raman analysis shows that the initial ore‐forming fluids mainly belong to the CO₂‐H₂O‐NaCl system and gradually transferred to the H₂O‐NaCl system. The C‐type inclusions of Q1‐1 show the salinity of 3.1–10.1 (av. 6.9 ± 1.7) wt.% NaCl eqv., and the total homogenization temperature (T_h) of 305–391°C. The homogenization temperature decreases gradually from the early to the late stage, with insignificant change in salinity, indicating that fluid cooling is the main precipitation mechanism. Trapping pressures of C‐type FIs are estimated at 206–284 MPa and 203–211 MPa for the early and middle stages, corresponding to the mineralization depths of 7.2–9.9 km and 7.1–7.4 km, respectively. The FIs in the early stage indicate that the initial ore‐forming fluids are characterized by low salinity and CO₂ richness, which are different from those of the intrusion‐related gold deposits, but consistent with the orogenic gold deposits.

东天山是中亚增生造山带的重要组成部分, 蕴含了重要的铁、铜、镍、铅锌、金、钼、铷等矿床。近年来, 东天山地区陆续发现了十余个大中型钨矿床, 有望成为重要的钨矿资源基地。本文介绍了东天山地区钨矿床的地质特征、时空分布与构造背景, 总结了东天山钨矿成矿规律, 开展了成矿预测。东天山地区钨矿类型主要包括矽卡岩型、石英脉型及云英岩型, 钨矿床的空间分布明显受控于前寒武纪结晶基底, 成矿时间主要聚焦于三叠纪和晚石炭世。其中, 中天山地块的矽卡岩型钨矿和东南缘的石英脉型钨矿形成于三叠纪, 而中天山西南缘的矽卡岩型钨矿形成于晚石炭世, 均与洋盆闭合之后的碰撞造山作用有关。根据东天山地区钨矿成矿规律, 本文认为东天山地区钨矿找矿潜力巨大, 提出了"前寒武纪基底+花岗岩+化探异常"的钨矿找矿预测思路, 针对不同尺度的钨矿找矿勘查提出了建议。

The Liushuping deposit, located on the northeast margin of the Bikou Block, is the middle-sized gold-zinc deposit (with ore reserves of 15.67 × 10⁴ t Zn and 2.2 t Au) in the Mianxian–Lueyang–Yangpingguan area. The orebodies occur in the meta-dolomite of the Duantouya and Jiudaoguai formations controlled by the Jiudaoguai syncline. The ore-forming process has experienced hydrothermal period and epigenetic oxidation period, and the hydrothermal period can be divided into two stages. The hydrothermal sericite sample collected from stage 2 yielded a well-defined ⁴⁰Ar/³⁹Ar isotopic plateau age of 215.70 ± 0.37 Ma, and an ³⁹Ar/³⁶Ar-⁴⁰Ar/³⁶Ar normal isochron age of 215.35 ± 0.38 Ma, indicating that the metallogenic age of the Liushuping is the Late Triassic (ca. 215 Ma). The I_Sr(t) of sphalerite is higher than that of the Bikou Group but similar to the Duantouya Formation, indicating that the ore-forming fluids may mainly originate from the metamorphic dehydration of the Duantouya Formation. The Liushuping Au–Zn deposit is consistent with that of the Qinling Indosinian orogeny and mineralization, which are related to oceanic subduction during the Late Triassic.