滇中九龙方解石矿床成因——来自方解石矿物化学、流体包裹体、C-O同位素组成和U-Pb年代学的证据  

Genesis of the Jiulong calcite deposit in Central Yunnan Province,SW China:Evidence from mineral chemistry,fluid inclusions,C-O isotopic composition and U-Pb geochronology

作　　者：周红琳 魏爱英[1] 王维 张佳慧 薛传东[1] ZHOU Hong-lin;WEI Ai-ying;WANG Wei;ZHANG Jia-hui;XUE Chuan-dong(Department of Earth Sciences,Kunming University of Science and Technology,Kunming 650093,China)

机构地区：[1]昆明理工大学地球科学系,云南昆明650093

出　　处：《岩石矿物学杂志》2024年第6期1431-1447,共17页Acta Petrologica et Mineralogica

基　　金：第二次青藏高原综合科学考察研究(2021QZKK0301);国家自然科学基金项目(42003036,42163007,41373049);云南省新一轮找矿行动暨地勘基金项目(Y202405)。

摘　　要：九龙方解石矿床位于扬子地台西南缘滇中古生代盆地北西部,是滇中地区迄今发现的唯一一个大型巨晶方解石矿床,其成因目前尚不明确。本文选取由矿体内至围岩依次出现的巨晶方解石矿石、白云石化带以及近矿灰岩中的团块状方解石为对象,在地质调查、岩相学观测的基础上,分别对不同分带的方解石及围岩进行了矿物化学、C-O同位素组成及流体包裹体分析,并开展了矿石方解石U-Pb定年。结果显示,九龙方解石矿床主要矿体顺层产出,部分以大脉状赋存于顺层及高角度切层的断裂带中,下二叠统茅口组(P_(1)m)中上部层位灰岩是主要赋矿围岩,NE-SW向文林复向斜两翼及次级的"穹-盆"构造过渡部位是有利的赋矿部位,热液交代充填成矿、构造控矿特点突出,属后生低温热液型矿床;成矿流体为Cl-Na·Ca型盆地卤水,成矿物质主要源自赋矿围岩和下伏地层的循环作用,并存在深部岩浆热液的贡献;温度变化小、成核速率缓慢、结晶时间长是巨晶方解石大规模成矿的主要机制;其成矿时代为36.0±4.0 Ma(始-渐新世)。因而,九龙方解石矿床的成矿是喜马拉雅期区域性盆地流体活动的产物,代表了新生代印度-欧亚大陆碰撞造山作用在滇中古生代盆地的远程响应。The large Jiulong calcite deposit,located at the northwest part of Central Yunnan Paleozoic Basin in southwest margin of the Yangtze platform,is the only giant crystal calcite deposit discovered so far in central Yunnan Province,SW China.The ore genesis is still unclear.In this paper,based on geological investigation and petrographic observation,the giant crystal calcite ore zone,dolomitic rock zone,and mottled calcilization rock zone are selected to carry out mineral chemistry,C-O isotopic composition and fluid inclusion analysis of different types of calcites and ore-hosting rocks,and calcite U-Pb dating.The results show that the proved orebodies are mainlyhosted along the beddings of the hosting limestones in the stratiform shape,and others exist in the bedding horizons and steeply dipping fault fracture zones in the form of large vein types.Both limbs of the NE-SW-extending Wenlin syncline and the transitional segments of the secondary"dome-and-basin"structure are favorable ore-depositional areas.And the middle and upper successions of the Lower Permian Maokou Formation(P_(1)m)limestone are the main ore-hosting rocks.The Jiulong calcite deposit is of low-temperature epigenetic origin deposit with prominent features of hydrothermal fluid replacement and filling and ore-structure controlling.The ore-forming fluid is featured by the Cl-Na·Ca type basin brine,and ore-formation materials and fluids are mainly originated from the cyclic interaction between the ore-hosting sediments and underlying basement sequences.There may be the addition of deep magmatic hydrothermal fluid.The small temperature variation,slow nucleation rate,and long-term crystallization process are the key mechanism of the ore-formation of giant crystal calcites.The metallogenic age of this deposit is 36.0±4.0 Ma,that is the Eocene-Oligocene times.Therefore,the ore-formation of the Jiulong calcite deposit is the evolutionary product of the regional tectonic-controlling basin fluid during the Himalayan age,representing the remote respondence t

关 键 词：矿物化学 C-O同位素组成 方解石U-Pb定年 后生热液成因 九龙方解石矿床 滇中古生代盆地 

分 类 号：P578.61[天文地球—矿物学] P595[天文地球—地质学]