摘要
老东寨-乌佐铅锌矿床位于湘西-黔东成矿带南段,乌寿Ⅱ号矿体为其主矿体之一,前人对该矿床的成因认识尚未明确。本文通过对乌寿Ⅱ号矿体矿物组合与主要矿石矿物闪锌矿微量元素地球化学行为进行了系统研究,以探究矿床的成因。乌寿Ⅱ号矿体中的闪锌矿在热液期分两阶段产出:早阶段闪锌矿(Sp1)为灰黄色、淡黄色居多,多见于角砾状矿石中;晚阶段闪锌矿(Sp2)为褐灰色、浅橙黄色闪锌矿,解理发育。乌寿Ⅱ号矿体中闪锌矿的微量元素LA-ICP-MS分析结果表明,两期闪锌矿主要富集Cu、Cd、Ge、Ga,而相对贫Mn、In。根据闪锌矿中主要成分的二元关系推测,两期闪锌矿中Cd的替代机制存在差异,Sp1中Cd的替代机制可能为:Cd^(2+)+Fe^(2+)↔2Zn^(2+)和Cd^(2+)↔Zn^(2+);Sp2中Cd的替代机制可能为:Cd^(2+)+Fe^(2+)↔2Zn^(2+)。闪锌矿中Ge因价态不同会存在不同的替代机制,Sp1中Ge主要表现为Ge^(4+),以Ge^(4+)+2Cu+↔3Zn^(2+)的形式进入闪锌矿中,可能存在少量Ge^(2+),以Ge^(2+)+2Cu+↔2Zn^(2+)形式替代Zn^(2+);Sp2中Ge主要表现为Ge^(4+),替代方式有2Fe^(2+)+Ge^(4+)+↔4Zn^(2+)与4(Cu++Sb^(3+))+(Ge^(4+)+2Ag+)+2↔13Zn^(2+)等。Sp1与Sp2中Ga可能均主要以Cu++Ga^(3+)↔2Zn^(2+)的形式进入闪锌矿中。乌寿Ⅱ号矿体闪锌矿的形成温度相对较低,且Sp1(129~252℃,均值为177℃)的形成温度较Sp2(120~228℃,均值为149℃)略高。通过对比前人研究结果,本文认为老东寨-乌佐铅锌矿床乌寿Ⅱ号矿体的成因类型为密西西比河谷型(Mississippi-Valley-type,MVT)铅锌矿床。
The Laodongzhai-Wuzuo Pb-Zn deposit is located in the southern section of the Xiangxi-Qiandong metallogenic belt.The Wushou Ⅱ orebody is one of its main orebodies.The genesis of this deposit has not been clearly understood yet by previous researchers.This article systematically studied the mineral association of the Wushou Ⅱ orebody and geochemical behaviors of trace elements within the sphalerite,in order to explore the genesis of the deposit.The sphalerites in the Wushou Ⅱ orebody occurred in two hydrothermal stages.The early-stage sphalerite(Sp1)is mainly light yellow and grayish yellow sphalerite,which occurred commonly in brecciated ores.The late-stage sphalerite(Sp2)is brownish grey and light brownish yellow sphalerite with completed cleavages.The LA-ICP-MS analytical results of trace elements in sphalerites from the Wushou Ⅱ orebody show that sphalerites of two stages are mainly enriched in Cu,Cd,Ge,and Ga,but relatively depleted in Mn,and In.Based on the binary relationships of main components in sphalerites,it is inferred that there is difference between the substitution mechanism of Cd in Sp1 and that of Cd in Sp2.The substitution mechanism of Cd in Sp1 may be Cd^(2+)+Fe^(2+)↔Zn^(2+)and/or Cd^(2+)↔Zn^(2+),while that of Cd in Sp2 may be Cd^(2+)+Fe^(2+)↔2Zn^(2+).Ge in sphalerite could have different substitution mechanisms due to its different valence states.Ge occurred mainly as Ge^(4+)in Sp1 for substituting Zn^(2+),with the substitution mechanism of Ge^(4+)+2Cu+↔3Zn^(2+).A small amount of Ge occurred as Ge^(2+)in Sp1 for substituting Zn^(2+)with the substitution mechanism of Ge^(2+)+2Cu+↔2Zn^(2+).However,Ge occurred as Ge^(4+)in Sp2 for substituting Zn^(2+),with the substitution mechanisms of 2Fe^(2+)+Ge^(4+)+□↔4Zn^(2+)and/or 4(Cu++Sb^(3+))+(Ge^(4+)+2Ag+)+2□↔13Zn^(2+).Ga occurred as Ga^(3+)in both Sp1 and Sp2 for substituting Zn^(2+),with the substitution mechanism of Cu++Ga^(3+)↔2Zn^(2+).The formation temperatures of sphalerites in the Wushou Ⅱ orebody are relatively low.The formation temperatures of Sp1 crystals(129-252℃,average 177℃)are slightly higher than that of Sp2 crystals(120-228℃,average 149℃).By comparing previous research results,it is believed that the genetic type of the Wushou Ⅱ orebody in the Laodongzhai-Wuzuo Pb-Zn deposit belongs to the MVT type of Pb-Zn deposit.
作者
冯琪威
孟郁苗
徐争启
黄小文
FENG Qiwei;MENG Yumiao;XU Zhengqi;HUANG Xiaowen(College of Earth and Planetary Sciences,Chengdu University of Technology,Chengdu Sichuan 610059,China;State Key Laboratory of Critical Mineral Research and Exploration,Institute of Geochemistry,Chinese Academy of Sciences,Guiyang Guizhou 550081,China)
出处
《矿物学报》
2026年第2期236-249,共14页
Acta Mineralogica Sinica
基金
国家自然科学基金资助项目(编号:U23A2027、42473080、42073043)
贵州省基础研究计划重点项目(编号:黔科合基础-ZK[2023]重点050)。
