Mineralogy, temporal and spatial distribution of Mo mineralization in Guilinzheng Mo-W deposit, Jiangnan W mineralization belt and its significance

Abstract

安徽桂林郑钼钨矿床位于江南钨矿带北部，是目前区内唯一钼储量达到大型的钼钨矿床。本文在对该矿床地质特征和已有成果总结基础上，详细观察了各代表性矿化蚀变样品的岩相学特征，提出该矿床具镁质矽卡岩矿床特征，是桂林郑花岗斑岩熔体与奥陶系白云质灰岩地层交代的产物。矿石类型可分为靠近岩体（<100m）浸染状矿石和远离岩体（>100m）的条带状矿石，分别赋存在接触交代矽卡岩和层控矽卡岩中。桂林郑矿床的矿石矿物为富钼白钨矿（钼钙矿-白钨矿系列），可分为三个世代，分别形成于无水矽卡岩阶段（Sch-I）和含水矽卡岩-氧化物阶段（Sch-II和Sch-III），辉钼矿仅在浸染状矿石富钼白钨矿（Sch-III）边部少量发育。不同矿石类型、不同世代富钼白钨矿的电子探针成分分析显示，富钼白钨矿的钼含量（MoO₃%）在5.75%~71.02%之间，均值为46.00%（n=224），总体具有超常富钼的特点；从无水矽卡岩阶段到含水矽卡岩-氧化物阶段（早→晚）、从浅部的条带状矿石到深部的浸染状矿石（浅→深），富钼白钨矿MoO₃含量有降低趋势。桂林郑钼钨矿床是首个以富钼白钨矿为主要矿石矿物的钼-多金属矿床，这一特殊钼钨矿床的发现深化了矽卡岩钼钨矿床的成因认识，同时对江南钨矿带内区域成矿规律与找矿勘探工作的推进提供了依据。;The Guilinzheng Mo-W deposit is located in the northern sector of the Jiangnan W mineralization belt (JWB), which is the largest molybdenum-poly-metallic deposit in JWB at present. Based on the understanding of the geological background and previous studies of the Guilinzheng Mo-W deposit, the authors systematically observed the petrographic characteristics of various mineralization and alteration samples, which showed that it is a Mg-rich skarn deposit. This deposit was formed by metasomatism between the Guilingzheng granite porphyry melt and Ordovician dolomitic limestones. It can be classified as disseminated and banded ore types, which occur in the contact metasomatic skarn (<100m to the granite porphyry) and strata bound skarn (>100m to the granite porphyry), respectively. The main ore mineral is Mo-rich scheelite (powellite-scheelite series), which can be subdivided into 3 stages in order:the first-stage Mo-rich scheelite (Sch-I) was formed during anhydrous skarnization; the two later ones (Sch-II and Sch-III) were both formed during hydrous skarnization. There are some molybdenite occurring in the edges and gaps of the Sch-III grains. The EPMA results of those different types Mo-rich scheelite showed that the MoO₃ contents varied from 5.75% to 71.02%, with an average value of 46.00% (n=224), indicating an extremely high-Mo ore mineral. Decreasing MoO₃ contents of Mo rich scheelite in Guilinzheng deposit is observed from shallow banded ore to deep disseminated ore spatially, and from early anhydrous skarn stage to late hydrous skarn stage temporally. Guilinzheng Mo-W deposit is the firstly reported Mo deposit with Mo-rich scheelite, instead of molybdenite as the main ore mineral. Systematic studies of this ore deposit can deepen the genetic understanding of the powellite-scheelite mineralization and promote researches on the regional metallogeny and prospecting indicators in JWB.