内蒙古大井铜锡多金属矿床矿石中Cu-S同位素特征及成矿预测

doi:10.13745/j.esf.sf.2021.11.5

摘要/Abstract

摘要：

内蒙古大井铜锡多金属矿床是大兴安岭成矿带代表性矿床之一,矿区位于内蒙古东部林西县境内,成矿地质条件良好。矿床矿石中同位素特征及与成矿的关系研究薄弱。本文通过对矿体中黄铜矿Cu同位素,黄铜矿、黄铁矿S同位素和Pb同位素的研究表明:黄铜矿δ⁶⁵Cu 值总体范围为 -0.46‰+0.32‰,平均值为0 ‰,2σ误差平均值约为0.03‰;黄铜矿、黄铁矿δ³⁴S值总体范围为 +0.076 ‰+3.00‰,平均值为+1.83‰,且δ³⁴S值分散程度也较小,整体较均一,属于岩浆硫的同位素特征;Pb同位素数据整体变化很小,具体为²⁰⁶Pb/²⁰⁴Pb=18.29118.353,²⁰⁷Pb/²⁰⁴Pb =15.50115.574,²⁰⁸Pb/²⁰⁴Pb =38.05138.265。结合区域前人的研究表明,大井矿Cu同位素的变化是由于硫化物-岩浆分异过程导致,大井矿矿石黄铜矿δ⁶⁵Cu的变化可能指示了矿化阶段成矿硫化物的演化方向,δ⁶⁵Cu逐渐降低的方向可能存在隐伏矿体,研究区域东部生产区域与外围预测未生产区域具有一致的Cu同位素特征,Cu同位素证据表明大井矿外围预测区可能存在深部隐伏矿体。

关键词: 大井矿, 铜锡多金属矿床, Cu同位素, S同位素, 隐伏矿体

Abstract:

The Dajing Sn-Cu polymetallic deposit in Inner Mongolia represents typical ore deposits in the Daxinganling metallogenic belt. The mining area is located in Linxi County, eastern Inner Mongolia, with geological conditions favorable for ore formation. Here, we studied Cu isotopes in chalcopyrite and S and Pb isotopes in chalcopyrite and pyrite orebodies. The measured δ⁶⁵Cu value for chalcopyrite ranged from -0.46‰ to +0.32‰ overall, averaging at 0‰ with an average 2σ error of 0.03‰; the δ³⁴S values for chalcopyrite and pyrite ranged from +0.076‰ to +3.00‰ overall, averaging at +1.83‰, with relatively high uniformity, showing magma associated S isotopic characteristics. The ranges of Pb isotopic ratios were small overall; specifically, ²⁰⁶Pb/²⁰⁴Pb ranged between 18.291-18.353, ²⁰⁷Pb/²⁰⁴Pb between 15.501-15.574, and ²⁰⁸Pb/²⁰⁴Pb between 38.051-38.265. Together with previous studies in the region we show that, in the Dejing deposit, Cu isotopic changes occur during the sulfide-magma differentiation process. The δ⁶⁵Cu variation pattern in chalcopyrite may indicate the direction of evolution of ore-forming sulfides in the mineralization stage. For instance, the direction of gradual δ⁶⁵Cu value decreasing may point to concealed orebody. In the study area of the Dejing deposit, the mining district in the east shares similar Cu isotopic characteristics with the non-production target area of its periphery, where, according to Cu isotope evidence, may exist deep concealed orebodies.

Key words: Dajing deposit, Cu-Sn polymetallic deposit, Cu isotope, S isotope, concealed orebody

中图分类号:

王跃, 苏尚国, 张旗, 周奇明, 张雅南. 内蒙古大井铜锡多金属矿床矿石中Cu-S同位素特征及成矿预测[J]. 地学前缘, 2022, 29(3): 319-328.

WANG Yue, SU Shangguo, ZHANG Qi, ZHOU Qiming, ZHANG Yanan. Cu-S Isotope characteristics and metallogenic prediction of orebodies in the Dajing Sn-Cu polymetallic deposit in Inner Mongolia[J]. Earth Science Frontiers, 2022, 29(3): 319-328.

图/表 5

图1 大兴安岭南段区域地质图(a)和大井矿区域地质图(b)(a据文献[21];b据文献[29⇓-31])

Fig.1 Regional geological maps of the (a) southern section of Daxinganling (adapted from [21]) and (b) Dajing deposit (adapted from [29⇓-31])

图2 内蒙古大井铜锡多金属矿床46线剖面示意图(据文献[32])

Fig.2 Schematic diagram of section 46 of the Dajing Cu-Sn polymetallic deposit in Inner Mongolia. Adapted from [32].

图3 内蒙古大井铜锡多金属矿床矿硫化物矿石结构特征 (a)—硫化物矿体与粉砂质泥岩接触关系;(b)—镜下黄铜矿与黄铁矿和磁铁矿共存。CCp—黄铜矿;Py—黄铁矿;Mag—磁黄铁矿。

Fig.3 Structural characteristics of sulfide orebody in the Dajing Cu-Sn polymetallic deposit, Inner Mongolia

表1 大井矿铜锡多金属矿床主矿体硫化物矿物铜同位素、硫同位素和铅同位素组成

Table 1 Cu, S, Pb Isotope compositions of sulfide minerals in the main orebody of the Dajing Cu-Sn polymetallic deposit

样品编号	矿物	采样位置	δ⁶⁵Cu/‰	2σ/‰	δ³⁴S/‰	²⁰⁶Pb/²⁰⁴Pb	²⁰⁷Pb/²⁰⁴Pb	²⁰⁸Pb/²⁰⁴Pb
10#01-1	黄铁矿	矿体			2.638	18.351	15.574	38.094
10#01-2	黄铜矿	矿体	-0.446	0.034	1.975	18.346	15.561	38.191
10#02-1	黄铁矿	矿体			2.638
10#02-2	黄铜矿	矿体	0.178	0.056	2.966	18.301	15.509	38.105
10#03-1	黄铁矿	矿体				18.341	15.512	38.256
10#03-2	黄铜矿	矿体	0.326	0.024	0.806	18.291	15.492	38.046
10#04-1	黄铁矿	矿体			3.842
10#04-2	黄铜矿	矿体	0.127	0.008	2.860	18.318	15.501	38.136
10#05-1	黄铁矿	矿体			1.236
10#05-2	黄铜矿	矿体	0.028	0.044	2.942	18.373	15.534	38.156
10#06-1	黄铁矿	矿体			1.049	18.279	15.508	38.051
10#06-2	黄铜矿	矿体	0.163	0.054	0.441	18.345	15.527	38.104
10#07-1	黄铁矿	矿体			2.240	18.336	15.534	38.154
10#07-2	黄铜矿	矿体	-0.458	0.030		18.315	15.546	38.174
10#08-1	黄铁矿	矿体
10#08-2	黄铜矿	矿体	-0.289	0.023	0.563	18.318	15.508	38.164
10#09-1	黄铁矿	矿体			1.150
10#09-2	黄铜矿	矿体	0.177	0.033	1.070	18.294	15.561	38.167
10#10-1	黄铁矿	矿体			2.553
10#10-2	黄铜矿	矿体	0.139	0.037	0.076	18.353	15.515	38.195

图4 应用65Cu变化预测内蒙古大井铜锡多金属矿床隐伏岩体示意图(底图据文献[32])

Fig.4 Illustration of using 65Cu isotope in metallogenic prediction of concealed rock mass in the Dajing Cu-Sn polymetallic deposit, Inner Mongolia, through spatial association between the direction of gradual δ65Cu value decreasing with IP anomaly and occurrences of orebody and concealed rock mass in deep fault zones. Basemap adapted from [32].

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