ZIRCON U-Pb CHRONOLOGY, GEOCHEMISTRY AND PETROGENESIS OF ORE-BEARING GRANODIORITE IN TSAV SILVER POLYMETALLIC DEPOSIT, MONGOLIA
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摘要:
中蒙边境查夫-甲乌拉银多金属矿集区内与成矿相关的岩浆岩研究薄弱. 以查夫银多金属矿床含矿花岗闪长岩及其闪长质包裹体为研究对象, 进行了岩石学、锆石U-Pb年代学、地球化学和原位Lu-Hf同位素研究. 花岗闪长岩及闪长质包裹体的锆石206Pb/238U加权平均年龄分别为195.7±1.3 Ma和196.5±2.4 Ma, 在误差范围内一致, 为早侏罗世岩浆作用的产物. 寄主花岗闪长岩为准铝质-弱过铝质、高钾钙碱性-钙碱性系列的I型花岗岩, 闪长质包裹体为同源岩浆混合成因包裹体. 寄主花岗闪长岩具有宽泛的εHf(t)值(4.4~10.7), 其二阶段Hf模式年龄介于550~960 Ma, 表明寄主花岗闪长岩的初始岩浆起源于新元古代从亏损地幔增生的新生地壳的部分熔融, 并存在幔源物质的混入. 基于以上研究, 结合区域构造演化资料, 认为查夫银多金属矿床含矿花岗闪长岩形成于蒙古-鄂霍次克洋板块俯冲的活动大陆边缘背景.
Abstract:The research on magmatic rocks related to mineralization was weak in Tsav-Jiawula Ag polymetallic ore concentration area on the China-Mongolia border. Taking the ore-bearing granodiorite and its dioritic enclaves in Tsav Ag polymetallic deposit as object, the paper studies the petrology, zircon U-Pb chronology, geochemistry and in-situ Lu-Hf isotopes. The zircon 206Pb/238U weighted average ages of 195.7±1.3 Ma and 196.5±2.4 Ma for granodiorite and diorite enclaves respectively are consistent within the error range, indicating that both were products of the Early Jurassic magmatism. The host granodiorite belongs to I-type granite of quasi aluminous-weakly peraluminous and high K calc alkaline-calc alkaline series. The diorite enclaves are of consanguineous magma mixing origin. The host granodiorite has broad εHf(t) values (4.4-10.7) with the two-stage Hf model ages ranging from 550 to 960 Ma, reflecting the primary magma of host granodiorites originated from the partial melting of new crustal accretion from depleted mantle in Neoproterozoic with mantle-derived materials mixed. Combined with the regional tectonic evolution data, it is considered that the Tsav Ag polymetallic deposit was formed in the active continental margin setting caused by the subduction of Mongolia-Okhotsk oceanic plate.
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图 9 花岗闪长岩和闪长质包裹体K2O-Na2O、TFeO-MgO及LaN/YbN-δEu图解(b和c据文献[16])
Figure 9.
图 11 查夫银多金属矿床含矿花岗闪长岩及闪长质包裹体成岩模式图(据文献[9]修改)
Figure 11.
表 1 查夫-甲乌拉银多金属矿集区内银多金属矿床地质特征对比表
Table 1. Comparison of geological characteristics of deposits in Tsav-Jiawula Ag polymetallic ore concentration area
地质特征 查夫银多金属矿床* 乌兰银多金属矿床[3] 甲乌拉银多金属矿床[5-6] 赋矿地层 侏罗系沙里林组玄武岩、安山岩、粗面安山岩、英安岩、安粗岩和高钾流纹岩 侏罗系英安岩、安山岩、玄武岩和流纹岩 侏罗系上统玄武岩、安山岩、流纹岩、板岩和砂砾岩 侵入岩脉 早中生代侵入杂岩(花岗闪长岩、闪长岩、正长岩、花岗闪长岩等)、晚侏罗世侵入杂岩(辉长闪长岩、闪长岩、闪长玢岩等) 晚侏罗世石英斑岩(150.8±4.4 Ma) 晚侏罗世正长斑岩(148.8±2.2 Ma)、二长斑岩(145.3±1.9 Ma)、石英斑岩(150.1±1.8 Ma)及富碱花岗斑岩(146.4±1.6 Ma) 控矿构造 查夫断裂带内北西和近南北向断裂 北西向穆哈尔断裂 北西、北北西向断裂构造 矿体特征 呈脉状、透镜状或条带状产出于火山-沉积地层、早中生代岩浆杂岩体和晚侏罗世侵入杂岩内 主要呈脉状产出于火山-沉积地层、石英斑岩体以及构造破碎带内 多呈脉状,少量为透镜状,产出于火山-沉积地层内的北西西—北北西向断裂破碎带中 围岩蚀变 硅化、绢云母化、绿帘石化和碳酸盐化 绿帘石化、阳起石化、硅化、钾长石化、碳酸盐化、绿泥石化 硅化、绿泥石化、伊利石水白云母化、萤石化、碳酸盐化和青磐岩化 金属矿物 方铅矿和闪锌矿为主,其次为黄铁矿、黄铜矿、白铁矿、辉铜矿、铜蓝、辉银矿、自然铋和自然银 自然银、方铅矿、闪锌矿、黄铁矿为主,其次为黄铜矿、毒砂和磁黄铁矿 主要为方铅矿、闪锌矿、黄铁矿,其次为黄铜矿、磁黄铁矿、毒砂、磁铁矿以及辉银矿等含银矿物 脉石矿物 石英和方解石为主,次要矿物有绢云母、电气石、绿泥石等 石英、方解石、水白云母、萤石等 石英、方解石、萤石、绢云母、绿泥石、绿帘石 矿石结构 半自形粒状、他形粒状、嵌晶、溶蚀、交代残余结构等 半自形、他形粒状、交代残余、包含结构等 自形—半自形、他形粒状、充填、交代残余、包含、乳浊状、叶片状、碎裂、纤状、羽状、雏晶结构 矿石构造 块状构造、角砾状构造、细脉状构造和浸染状构造 块状构造、团块状构造、角砾状构造、浸染状构造、脉状构造等 块状构造、浸染状构造、细脉浸染状构造、团块状构造、脉状构造、不规则粒状构造、角砾状构造等 *资料来源于本研究及文献[10]. -
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