陕西池沟Cu-Mo矿床新发现花岗岩脉的年代学研究及其地质意义

Geochronology and geological significance of newly discovered granitoid dikes in Chigou Cu-Mo deposit, Shaanxi Province

中文关键词:斑岩-矽卡岩铜矿  细粒花岗岩脉  成矿作用  池沟矿床  东秦岭

keywords:porphyry-skarn copper ore  fine-grained granite dikes  mineralization  Chigou deposit  East Qinling

中文摘要:池沟是近年在东秦岭成矿带发现为数不多的中型斑岩-矽卡岩铜钼矿床，初步研究表明浅部铜矿体与晚中生代闪长质岩浆有关，但是否存在同一岩浆事件的不同演化阶段岩浆和相关矿化还不清楚。最近，矿区北部开展深钻孔ZK701（1615 m），在标高约573 m和-558 m均发现多层铜矿体和细粒花岗岩脉，矿体主要产于岩脉接触带的矽卡岩中。文章选择新揭露的细粒花岗岩开展锆石U-Pb定年和微量元素分析，并对矽卡岩中的代表性矿物进行EMPA成分分析。结果显示，池沟地区发育钙铁榴石（And_86-94Gro_0-8）+透辉石（Di_60-72Hd_26-38）的矿物组合，暗示其形成于氧化条件。细粒花岗岩的锆石U-Pb年龄为（146.3±5.7）Ma，与石英闪长斑岩成岩年龄接近，并发育早古生代和新元古代捕获锆石。锆石微量元素计算获得ΔFMQ=0.8~1.0和Eu_N/Eu_N^* > 0.4，暗示细粒花岗岩具有高氧逸度和含水量。通过综合研究，文章认为细粒花岗岩具有成铜潜力，并与石英闪长斑岩构成多阶段成岩成矿，推测该区具有形成大型铜矿的潜力。

Abstract:Chigou is one of the few medium-sized porphyry-skarn copper deposits recently discovered in the East Qinling metallogenic belt. Previous studies suggested that the shallow copper orebodies are genetically related to the Late Mesozoic dioritic magma, and it is unclear whether there are multiple stages of magmatism and mineralization. Recently, a deep drill hole ZK701 (1615 m) discovers numerous Cu orebodies and granitoid dikes around elevations of 573 m and -558 m in the northern part of the mining area. The orebodies are mainly hosted in the skarn contact zone around the fine-grained granite dikes. This paper chooses the fine-grained granite and skarn minerals for EMPA, zircon U-Pb dating and trace element analysis. The results indicate that the prograde skarns consist of andradite (And_86-94Gro_0-8)+diopside (Di_60-72Hd_26-38), suggesting an oxidizing formation state. The zircon U-Pb age of fine-grained granite is (146.3±5.7) Ma, which is close to the age of quartz diorite porphyry, and the Early Paleozoic and Neoproterozoic inherited zircons are developed. The calculation of zircon trace elements shows that ΔFMQ=0.8~1.0 and Eu_N/Eu_N^* > 0.4, suggesting the high oxygen fugacity and water content of fine-grained granite. Through comprehensive research, this paper proposes that fine-grained granite has the potential for copper, and forms multi-stage diagenesis and mineralization with quartz diorite porphyry, so the Chigou has the possibility of discovering larger-scale copper deposit.