In-situ U-Pb geochronology and trace element analysis for the scheelite and apatite from the deep seated stratiform-like W(Cu) ore of the Zhuxi tungsten deposit, northeastern Jiangxi Province

Abstract

钨和铜由于地球化学行为存在明显差异，导致二者通常很难同时发生大规模的成矿作用。然而，江南钨矿带却出现了以石门寺和朱溪为代表的钨（铜）矿床。本文对朱溪钨（铜）矿床中最为重要的铜矿化作用开展了研究，即对形成于新元古代浅变质岩与古生代碳酸盐岩不整合界面附近的似层状钨（铜）矿体进行了精细的矿物学微区原位测试分析。厘定了朱溪矿床深部似层状钨（铜）矿体中铜矿化的形成时代为150.2±2.4Ma，与朱溪矿床的钨矿化时代及钨矿化相关岩体的成岩时代近于一致；揭示了深部似层状钨（铜）矿体中白钨矿、磷灰石的形成与朱溪矿床成矿相关岩浆高程度结晶分异形成的残余岩浆热液流体相关；结合朱溪矿床高分异残余岩浆（流体）具有高度还原的特征，初步提出朱溪矿床成矿过程中，钨来自于高分异残余岩浆热液流体，而铜来自于岩浆热液流体对基底地层中铜元素的萃取。;Due to the obvious differences in geochemical behavior for tungsten and copper in magmatic systems, it is usually difficult to occurring large-scale Cu- and W-mineralization at the same time. However, tungsten (copper) deposits represented by Shimensi and Zhuxi deposits appear in the Jiangnan tungsten belt. This study focuses on the most important copper mineralization occurred in the Zhuxi W (Cu) deposit, which formed the stratiform-like W(Cu) ore body near the unconformity interface between the Neoproterozoic metamorphic rock and the Paleozoic carbonate rock. In situ micro-zone analysis have been performed on the scheelite and apatite from the stratiform-like W(Cu) ore body. The LA-ICP-MS U-Pb data on the apatite show a Lower intercept age of 150.2±2.4Ma on the Tera-Wasserburg concordia diagrams, which represents the copper mineralization in the stratiform-like W(Cu) ore body and is closely consistent with the tungsten mineralization age and the diagenetic age of the granitic rocks associated with tungsten mineralization. The geochemical characteristics of scheelite and apatite reveal that the formation of scheelite and apatite grains in the stratiform-like W(Cu) ore body is genetically associated with the residual magmatic hydrothermal fluids formed from the highly fractionated magma system that induced the tungsten mineralization of the Zhuxi deposit. In view of the highly fractionated residual magma system of the Zhuxi deposit is characterized by highly reductive features. This study preliminarily proposed that during the mineralization process of the Zhuxi deposit, tungsten is derived from the highly fractionated magmatic system, while copper comes from the extraction of the basement strata by the magmatic hydrothermal fluid.