鲁西地区矽卡岩型铜金矿He-Ar同位素测定及其地质意义--以沂南地区铜井式铜金矿为例

He-Ar Isotopic Determination of Skarn Type Copper Gold Deposits in Western Shandong and Its Geological Significance——Taking Tongjing Type Copper Gold Deposits in Yinan Area as an Example

铜井式铜金矿(包括铜井铜金矿、金场铜金矿)是鲁西地区发现和开采最早、矿化最普遍的矽卡岩型铜金矿。该文通过矿床的He-Ar同位素测试分析,并结合前人的H,O,S,C稳定同位素分析和年代学测试结果,对铜井式铜金矿成因及成矿机制进行探讨。研究认为,铜井式金矿主要形成于燕山晚期(128~121Ma),黄铁矿中流体包裹体的^(3 )He/^(4 )He值为0.112 9~0.120 9R/Ra,高于地壳物质值,低于典型地幔物质值;^(40 )Ar/^(36 )Ar=364.1~458.0,高于大气值,低于地幔值,成矿流体中存在来源于地壳的放射成因Ar;^(4 )He/^(40 )Ar=1.16~3.433,平均2.296 5,略高于地幔值(1.36~2.23),低于典型地壳值(6.4),表明成矿流体中存在地幔He,Ar;同时有地壳He,Ar加入。综上认为,矿床成矿物质和流体具有深源特征,应来自地幔或下地壳,金成矿主要是与燕山晚期浅成—超浅成中酸性侵入岩有关,这些侵入体在侵位过程中与古生代碳酸盐岩地层发生接触交代作用,形成矽卡岩型铜金矿床。

Tongjing type copper gold deposits(including Tongjing type copper gold deposit and Jinchang type copper gold deposit)are the earliest and most common mineralization of skarn type copper gold deposits in Luxi area.Based on the analysis of He-Ar isotopes,combining with stable isotopes analysis of H,O,S,C and chronological test results,the genesis and metallogenic mechanism of Tongjing type copper gold deposit have been discussed.It is regarded that Tongjing type gold deposits are mainly formed in late Yanshan period(128~121Ma).The 3He/4He value of fluid inclusions in pyrite is 0.1129~0.1209Ra,which is higher than the value of crustal material,but lower than the value of typical mantle material.40 Ar/36 Ar is 364.1~458.0,which is higher than atmospheric values,but lower than the mantle value.There are radioactive Ar comes from the crust in the ore-forming fluids.The value of 4He/40 Ar is 1.16~3.433,and the average value is 2.2965,which is slightly higher than the mantle value(1.36~2.23),but lower than the typical crustal value(6.4).It is showed that there are mantle He and Ar in the ore-forming fluids,together with the addition of crust He and Ar.Overview,it is regarded that the ore-forming materials and fluids of the deposit have deep-sourced characteristics.It should originate from the mantle or the lower crust.The gold mineralization is mainly related to the hypabyssal-super hypabyssal acid intrusive rocks in late Yanshan period.These intrusions have contact metasomatism with Paleozoic carbonate strata during the emplacement process,and form skarn type gold deposit.