Noble Gas and Stable Isotopic Constraints on the Origin of the Ag–Cu Polymetallic Ore Deposits in the Baiyangping Area,Yunnan Province,SW China

The Lanping basin, Yunnan province, SW China, is located at the juncture of the Eurasian and Indian Plates in the eastern part of the Tibetan Plateau. The Lanping basin, in the Sanjiang Tethyan metallogenic province, is a significant Cu–Ag–Zn–Pb mineralized belt in China that includes the largest sandstone‐hosted Zn–Pb deposit in the world, the Jinding deposit, as well as several Ag–Cu deposits (the Baiyangping and Jinman deposits). These deposits, with total reserves of over 16.0 Mt Pb + Zn, 0.6 Mt Cu, and 7,000 t Ag, are mainly hosted in Meso‐Cenozoic clastic rocks and are dominantly controlled by two Cenozoic thrust systems developed in the western and eastern segments of the basin. The Baiyangping, Babaoshan, and Hetaoqing ore deposits are representative of the epithermal base metal deposits in the Lanping basin. The microthermometric data show that the ore‐forming fluids for these deposits were low temperature (110–180 °C) and had bimodal distribution of salinity at moderate and mid to high salinities (approximately 2–8 wt.% and 18–26 wt.% NaCl equivalent). The C and O isotope data indicate that the ore‐forming fluids were related to hot basin brines. We present new He and Ar isotope data on volatiles released from fluid inclusions contained in sulfides and in barite in these three deposits. ³He/⁴He ratios of the ore‐forming fluids are 0.01 to 0.14 R/Ra with a mean of 0.07 Ra (where R is the ³He/⁴He ratio and Ra is the ratio for atmospheric helium). This mean value is intermediate to typical ³He/⁴He ratios for the crust (R/Ra = 0.01 to 0.05) and the ratio for air‐saturated water (R/Ra = 1). The mean ratio is also significantly lower than the ratios found for mantle‐derived fluids (R/Ra = 6 to 9). The ⁴⁰Ar/³⁶Ar ratios of the ore‐forming fluids range from 298 to 382 with a mean of 323. This value is slightly higher than that for the air‐saturated water (295.5). The ³He/⁴He ratios of fluids from the fluid inclusions imply that the ore‐forming fluid for the Baiyangping, Babaoshan, and Hetaoqing deposits was derived from the crust and that any mantle‐derived He was negligible. The content of the radiogenic Ar ranges between 0.2 to 20.4%, and the proportion of air‐derived ⁴⁰Ar averages 94.1%. This indicates that atmospheric Ar was important in the formation of these deposits but that some radiogenic ⁴⁰Ar was derived from crustal rocks. Based on these observations coupled with other geochemical evidence, we suggest that the ore‐forming fluids responsible for the formation of the Ag–Cu–Pb–Zn polymetallic ore deposits in the Baiyangping area of the Lanping basin were mainly derived from crustal fluids. The fluids may have mixed with some amount of air‐saturated water, but there was no significant involvement of mantle‐derived fluids.     

云县栗树街铜银矿矿体地质特征

铜银矿产于上三叠统小定西组玄武岩、安山玄武岩、安山玄武质凝灰角砾岩的构造破碎带中,局部为破碎带旁侧蚀变带、蚀变发育的方解石脉中。品位均较稳定。已发现矿化体5条。矿床成因为与火山岩有关的中温热液型铜银矿床。     

用边界元法计算平面分层埋入体的电磁散射

本文结合平面边界元法和平面多极子展开法,求解平面分层埋入体的电磁散射。这种方法具有高速、占用内存少的优点。     

金平阿德博铜镍矿区王家寨矿段矿床成因探讨

矿床与华力西期超基性一基性一中性岩浆杂岩关系密切,成矿专属性明显。先期矿浆在杂岩体中初步熔离富集,后期矿浆在压力作用下沿断裂贯入,经期后热液改造再富集成矿。     

中甸雪鸡坪斑岩铜矿地质及找矿远景

雪鸡坪斑岩铜矿含矿母岩为印支期浅成相同熔型石英二长闪长玢岩、石英闪长玢岩、石英二长斑岩组成的复式岩株。发育面型蚀变带,经历气成一高温热液、中低温热液及低温热液三次矿液叠加成矿。在钾化带及石英一绢云母化带发育浸染状及网脉状铜矿化。认为普朗及其南部、地苏嘎是区内形成大型斑岩铜矿最有希望地区。     

Variation of copper isotopes in chalcopyrite from Dabu porphyry Cu-Mo deposit in Tibet and implications for mineral exploration

The study presents copper (Cu) isotope data of mineral separates of chalcopyrite from four drill core samples in the Miocene Dabu porphyry Cu-Mo deposit formed in a post-collisional setting in the Gangdese porphyry copper belt, southern Tibet. Copper isotope values in hypogene chalcopyrite range from –1.48‰ to +1.12‰, displaying a large variation of up to 2.60‰, which demonstrates Cu isotope fractionation at high-temperature during hydrothermal evolution. The majority of measured chalcopyrite isotopic compositions show a gradual increasing trend from –1.48‰ to +1.12‰ with the increase of drilling depth from 130m to 483m, as the alteration assemblages change from potassic to phyllic. Similarly, the other δ⁶⁵Cu values (δ⁶⁵Cu = ((⁶⁵Cu/⁶³Cu)_sample/(⁶⁵Cu/⁶³Cu)_standard − 1) × 1000) of the chalcopyrite show a gradual increasing trend from −1.48‰ to +0.59‰ with the decrease of drilling depth from 130 m to 57 m, as the alteration assemblages change from potassic, phyllic, through argillic to relatively fresh. These observations suggest a genetic link between Cu isotope variation and silicate alteration assemblages formed at different temperatures, indicative of a Rayleigh precipitation process resulting in the large variation of δ⁶⁵Cu values at Dabu. In general, samples closest to the center of hydrothermal system dominated by high-temperature potassic alteration are isotopically lighter, whereas samples dominated by low-temperature phyllic alteration peripheral to the center are isotopically heavier. The predicted flow pathways of hydrothermal fluids are from No. 0 to No. 3 exploration line, and the lightest δ⁶⁵Cu values are the most proximal to the hydrothermal source. Finally, we propose that the northwest side of the No. 0 exploration line has high potential for hosting undiscovered orebodies. The pattern of Cu isotope variation in conjunction with the features of silicate alteration in porphyry system can be used to trace the hydrothermal flow direction and to guide mineral exploration.     

Organic material accumulation of Carnian mudstones in the North Qiangtang Depression,eastern Tethys: Controlled by the paleoclimate,paleoenvironment, and provenance

The Late Triassic mudstones are considered to be the most significant hydrocarbon source rocks (TOC: 0.54%–3.29%) in the North Qiangtang Depression, eastern Tethys. Here, we present geochemical data from the Woruo Mountain Carnian mudstones, in order to investigate their paleoclimate, paleoenvironment, and provenance and to analyze the mechanism of organic material accumulation. The paleoclimate condition was warm and humid during the Carnian mudstones deposition, as indicated by moderate chemical index of alteration (CIA; 73–76), which may be connected with the Late Triassic Carnian stage global climate event in the Tethys. The low U/Th (0.17–0.25) and C_org/P_tot (7–33) ratio values and moderate manganese contents, reflect the oxidizing conditions during the Carnian mudstones deposition. The relatively high primary productivity in this study is supported by the relatively high P concentrations. The Al₂O₃–(CaO* + Na₂O)–K₂O ternary plot and Th/Sc–Zr/Sc crossplot reflect that the source areas have undergone a medium chemical weathering with weak sedimentary recycling. The TiO₂–Zr, Co/Th–La/Sc, La/Th–Hf, and La/Yb–∑REE bivariate diagrams indicate that the provenance of Carnian mudstones was primarily from felsic igneous rocks. The collision setting has been identified based on the multi-major elements discriminate plots in the present study. The Riwanchaka and Mayigangri masses to the southwest and south of the study area consisting mainly of Middle-Triassic granodiorite and Late-Triassic granite are likely responsible for supplying provenance to the Woruo Mountain Carnian mudstones, which have similar REE patterns. The relatively high TOC contents of Carnian mudstones are related to high paleoproductivity and fast sedimentation rates, which will lead to preservation of some organic matter even when bottom waters are completely oxidizing. The detrital input during the Carnian mudstones deposition would result in dilution of organic matter.     

铜陵地区的镶嵌构造及其控矿意义

铜陵地区是我国著名的铁铜矿区。海西—印支期,环太平洋波浪引起了北东向展布的褶皱群,其背斜是波峰带,向斜是波谷带。印支期,古地中海地壳波浪使本区形成了北西向断裂。北东向构造和北西向构造的交织,形成了区内镶嵌构造格局。北西向断裂控制着铜铁矿床的分布,铅锌矿床则沿北东向的背斜翼部分布,构造的等间距性决定着矿田分布的等间距性。     

安徽铜山铜(金)矿床锆石U-Pb年代学和Hf同位素地球化学

安徽池州的铜山岩体是长江中下游地区沿江岩浆岩主带中的含矿岩体之一,其形成年龄及岩石成因尚存在争议。该岩体主要由石英闪长玢岩、石英二长斑岩和花岗闪长岩组成,与铜金矿化关系密切。对铜山矽卡岩型铜(金)矿床的花岗闪长岩开展了锆石U-Pb定年和Hf同位素地球化学研究。岩石地球化学及同位素年代学研究结果表明:花岗闪长岩侵入年龄为(146.3±3.2)Ma,形成于早白垩世;锆石εHf(t)值平均为-5.23,说明铜山侵入岩具有壳幔混合的岩浆岩源区性质;锆石的二阶段Hf模式年龄分布在1 184.51~1 422.72Ma之间,说明岩浆源区与皖南地区出露的中元古代基底有密切关系。构造判别图解显示,铜山岩体属火山弧花岗岩,与长江中下游铜金矿床含矿岩体形成于同一构造背景下,据此推测铜山地区大地构造背景形成于与古太平洋板块俯冲密切相关的大陆边缘岩浆弧环境。     

云南兰坪科登涧构造热液型铜多金属矿

铜矿赋存于上三叠统小定西组中段变质火山岩中,圈出两条铜矿体,分别受F1和F2压扭性断层破碎带控制,似层状产出.金属硫化物大多呈大斑块状集合体密集分布,属与脆韧性断裂有关的构造热液型铜多金属矿床.