投稿时间：2022-04-22
修订日期：2023-03-11
网络发布日期：2023-05-06
中文摘要:喇嘛苏矿床是中国西天山地区首例大型铜矿床，矿体主要产于花岗闪长斑岩与碳酸盐岩的接触带矽卡岩中。石榴子石在矽卡岩中大量发育，是矽卡岩的主要造岩矿物，分为外矽卡岩带红棕色粗粒石榴子石（Grt-Ⅰ）、外矽卡岩带浅棕色细粒石榴子石（Grt-Ⅱ）、外矽卡岩带黄绿色不等粒石榴子石（Grt-Ⅲ）3类。文章对不同产状石榴子石开展了电子探针分析和LA-ICP-MS原位微区分析，探讨了石榴子石成因及其对成矿过程的指示。喇嘛苏矿床内3类石榴子石均以钙铁榴石为主，其次为钙铝榴石，具有相似的微量元素组成，亏损Rb、Ba、Sr等大离子亲石元素，富集Th、U、Nb、Ce高场强元素。3类石榴子石的稀土元素特征差别较大，其中，Grt-Ⅰ类石榴子石的∑REE为101.47×10-6~262.87×10-6，具有较陡峭的REE配分模式，LREE/HREE为3.81~68.50，具有正Eu异常；Grt-Ⅱ类石榴子石核部的∑REE为163.49×10-6~249.52×10-6，显示负Eu异常，LREE/HREE为2.00~4.71，而外环带的∑REE为46.34×10-6~99.99×10-6，显示正Eu异常，LREE/HREE为18.06~177.23；Grt-Ⅲ类石榴子石的∑REE为31.71×10-6~219.02×10-6，具有平坦的REE模式分配，显示正Eu异常，LREE/HREE为2.16~9.07。研究结果表明，喇嘛苏成矿流体系统是从开放体系趋向封闭体系进行演化，流体从渗滤交代演变为扩散交代，依次形成Grt-Ⅰ类、Grt-Ⅱ类和Grt-Ⅲ类石榴子石。3类石榴子石总体上形成于相对氧化的流体中，而流体的高氧逸度能够抑制Cu以硫化物的形式过早沉淀，有利于Cu在岩浆热液中运移和聚集，最终提高早期岩浆热液的成矿潜力。
Abstract:The Lamasu deposit is the first large copper deposit discovered in Chinese western Tianshan. Its ore bodies mainly occur in skarn formed in contact zone between granodiorite porphyry and carbonate strata. Garnet, as a major component of skarn, abundantly develops in skarn at Lamasu. The garnets include three types:red-brown coarse garnet in exoskarn (Grt-Ⅰ), light brown fine-grained garnet in exoskarn (Grt-Ⅱ), and yellow-green heterogranular garnet in exoskarn (Grt-Ⅲ). In this paper, electron probe analysis and LA-ICP-MS in-situ microanalysis of different garnets are carried out to discuss garnet genesis and its implication for the metallogenic process. The three types of garnets from the Lamasu deposit are mainly andradite with minor grossularite. These garnets have similar trace element compositions and exhibit LILE-depletion (e.g., Rb, Ba and Sr) and HFSE-enrichment (e.g., Th, U, Nb and Ce). The three types of garnets show different REE compositions. The ∑REE of Grt-Ⅰ garnet range from 101.47×10-6 to 262.87×10-6 and show a steep REE distribution pattern with LREE/HREE from 3.81 to 68.50 and positive Eu anomaly. The ∑REE in core area of Grt-Ⅱ garnet range from 163.49×10-6 to 249.52×10-6, showing negative Eu anomaly, the LREE/HREE ranges from 2.00 to 4.71. The ∑REE in outer ring of Grt-Ⅱgarnet range from 46.34×10-6 to 99.99×10-6, and its LREE/HREE is 18.06~177.23, showing positive Eu anomaly. The ∑REE of Grt-Ⅲ garnet range from 31.71×10-6 to 219.02×10-6, with flat REE distribution pattern and positive Eu anomaly, and the LREE/HREE ranges from 2.16 to 9.07. This study shows that the Lamasu ore-forming fluid system evolved from an open system to closed system, infiltration metasomatism to diffusive metasomatism, and successively form Grt-Ⅰ, Grt-Ⅱ and Grt-Ⅲ garnets. The three types of garnets are generally formed in a relative oxidized fluid system. The high oxygen fugacity of the fluid can inhibit the premature Cu precipitation as sulfide, which favors for the Cu element migration and accumulation in the magmatic hydrothermal and improve early magmatic hydrothermal metallogenic potential.
keywords:geochemistry garnet skarn Lamasu West Tianshan
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基金项目:本文得到国家自然科学基金项目（编号：41672066、41820104010）、国家重点研发计划项目（编号：2017YFC0601403）、中央级公益性科研院所基本科研业务费项目（编号：KK2106、KK2205）和国家留学基金委访问学者项目联合资助
引用文本：
王晓彤,刘军,何军成,孙鹏.2023.新疆喇嘛苏铜矿床成因：来自石榴子石元素地球化学的证据[J].矿床地质,42(2):347~365WANG XiaoTong,LIU Jun,HEJunCheng,SUN Peng.2023.Genesis of Lamasu Cu deposit, Xinjiang: Constraints from garnet element geochemistry[J].Mineral Deposits42(2):347~365
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