紫金山金铜矿床是世界级的超大型矿床,具有上金下铜的分带特征,上部金矿已开采完毕,中下部铜矿体尚未圈闭,开展流体包裹体均一温度测量对确定成矿的热源中心和找矿方向研究具有重要的指导意义。本文在野外地质调查、流体包裹体样品采集、岩相学观察的基础上,对露天采矿场海拔560~580 m平台与铜矿体共生的蚀变石英、明矾石开展了流体包裹体均一温度和冰点温度的测量,结果表明:流体包裹体主要有液相包裹体、气相包裹体、CO2包裹体以及少量含子矿物多相包裹体4种类型;流体包裹体均一温度范围为120.9℃~430.1℃,主要集中于160℃~220℃和360℃~380℃,显示具有2个成矿温度峰值,可能暗示具有2次成矿作用;冰点温度−0.1℃~−13.0℃,对应盐度为0.18% NaCl eqv~16.89% NaCl eqv。根据流体包裹体均一温度中较高温度峰值绘制的流体包裹体均一温度等值线图显示成矿热源来自矿区的东南侧深部,并向南东方向倾伏,指示矿区东南侧深部仍具有较大的找矿前景。 The Zijinshan gold-copper deposit is a world-class super-large deposit with the zoning characteristics of upper gold and lower copper. The upper gold deposit has been mined, and the middle and lower copper ore bodies have not yet been trapped. The homogenization temperature measurement of fluid inclusions has important guiding significance for determining the heat source center and prospecting direction of mineralization. Based on field geological survey, fluid inclusion sample collection and petrographic observation, the homogenization temperature and freezing point temperature of fluid inclusions in altered quartz and alunite associated with copper ore bodies at an altitude of 560-580m in open-pit mining sites were measured. The results show that there are four types of fluid inclusions: liquid inclusions, gas inclusions, CO2inclusions and a small amount of daughter mineral-bearing multiphase inclusions. The homogenization temperature range of fluid inclusions is 120.9℃~430.1℃, mainly concentrated in 160℃~220℃ and 360℃~380℃, showing two mineralization temperature peaks, which may imply two times mineralizations. The freezing point temperature was −0.1℃~−13.0℃, and the corresponding salinity was 0.18% NaCl eqv~16.89% NaCl eqv. The homogenization temperature contour map of fluid inclusions drawn according to the higher temperature peak in the homogenization temperature of fluid inclusions shows that the ore-forming heat source comes from the deep part of the southeast side of the mining area and is inclined to the southeast direction, indicating that the deep part of the southeast side of the mining area still has great prospecting potential.
紫金山金铜矿床是世界级的超大型矿床,具有上金下铜的分带特征,上部金矿已开采完毕,中下部铜矿体尚未圈闭,开展流体包裹体均一温度测量对确定成矿的热源中心和找矿方向研究具有重要的指导意义。本文在野外地质调查、流体包裹体样品采集、岩相学观察的基础上,对露天采矿场海拔560~580 m平台与铜矿体共生的蚀变石英、明矾石开展了流体包裹体均一温度和冰点温度的测量,结果表明:流体包裹体主要有液相包裹体、气相包裹体、CO2包裹体以及少量含子矿物多相包裹体4种类型;流体包裹体均一温度范围为120.9℃~430.1℃,主要集中于160℃~220℃和360℃~380℃,显示具有2个成矿温度峰值,可能暗示具有2次成矿作用;冰点温度−0.1℃~−13.0℃,对应盐度为0.18% NaCl eqv~16.89% NaCl eqv。根据流体包裹体均一温度中较高温度峰值绘制的流体包裹体均一温度等值线图显示成矿热源来自矿区的东南侧深部,并向南东方向倾伏,指示矿区东南侧深部仍具有较大的找矿前景。
紫金山金铜矿床,流体包裹体,均一温度等值线,成矿热源
Xiaomin Yang, Yihang Fu, Dunpeng Li*
Zijin School of Geology and Mining, Fuzhou University, Fuzhou Fujian
Received: Mar. 1st, 2024; accepted: Apr. 5th, 2024; published: Apr. 15th, 2024
The Zijinshan gold-copper deposit is a world-class super-large deposit with the zoning characteristics of upper gold and lower copper. The upper gold deposit has been mined, and the middle and lower copper ore bodies have not yet been trapped. The homogenization temperature measurement of fluid inclusions has important guiding significance for determining the heat source center and prospecting direction of mineralization. Based on field geological survey, fluid inclusion sample collection and petrographic observation, the homogenization temperature and freezing point temperature of fluid inclusions in altered quartz and alunite associated with copper ore bodies at an altitude of 560-580m in open-pit mining sites were measured. The results show that there are four types of fluid inclusions: liquid inclusions, gas inclusions, CO2inclusions and a small amount of daughter mineral-bearing multiphase inclusions. The homogenization temperature range of fluid inclusions is 120.9℃~430.1℃, mainly concentrated in 160℃~220℃ and 360℃~380℃, showing two mineralization temperature peaks, which may imply two times mineralizations. The freezing point temperature was −0.1℃~−13.0℃, and the corresponding salinity was 0.18% NaCl eqv~16.89% NaCl eqv. The homogenization temperature contour map of fluid inclusions drawn according to the higher temperature peak in the homogenization temperature of fluid inclusions shows that the ore-forming heat source comes from the deep part of the southeast side of the mining area and is inclined to the southeast direction, indicating that the deep part of the southeast side of the mining area still has great prospecting potential.
Keywords:Zijinshan Copper-Gold Deposit, Fluid Inclusions, the Contour Map of the Homogenization Temperature, Ore-Forming Heat Source
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紫金山金铜矿床位于福建省西部,是世界著名的高硫化型浅成低温热液矿床,累计探明金储量超过316 t,铜储量超242万t [
前人对紫金山金铜矿床流体包裹体开展了大量卓有成效的工作,陈景河、张德全等对紫金山金铜矿床各蚀变带流体包裹体均一温度测定,获得温度范围介于100℃~420℃,具有3个温度峰值代表早、中、晚3期热液活动,热液性质由岩浆热液向次火山热液、热水溶液演化 [
紫金山金铜矿床位于我国东南部的华夏地块,构造位置位于福建西部的NW向上杭–云霄断裂带的上杭火山盆地东北约3 km (图1)。
矿区出露的地层主要包括早震旦世的楼子坝群、晚泥盆世的天瓦岽组和桃子坑组、早石炭世的林地组、早白垩世的石帽山群,以及第四系等 [
图1. 紫金山矿田地质简图 [
紫金山金铜矿床的矿体分为上部金矿带(约650 m~1138 m)和下部铜矿带(< 650 m)。上部金矿带以金矿体为主,由于铜矿物在浅成热液环境中易受风化作用的影响 [
下部铜矿带的铜矿体为隐伏矿体,自上而下为Ⅱ号矿化带、Ⅰ号矿化带、0号矿化带、Ⅺ号矿化带等,主要赋存于燕山早期的中细粒花岗岩和燕山晚期的隐爆角砾岩中。矿体在平面上自南西向北东斜列,脉带呈北北东–南西西向展布,总体走向为320˚,倾向北东。倾角在中浅部为10˚~20˚,中深部多为15˚~30˚。在剖面上呈右行侧列分布,侧伏角约为15˚~35˚。矿体主要分布于27线~16线,长1.2 km,宽1.1 km,展布面积为1.32 km2,普遍具有走向长度小于倾向延深的特点 [
铜矿石矿物种类多样,根据前人研究统计可达33种 [
围岩蚀变作用范围广、强度大,面积达数十平方千米,垂深超过1500 m,主要蚀变类型有硅化、绢云母化、地开石化、明矾石化。以火山通道相的英安斑岩为中心,向外或向下依次出现硅化带(石英 ± 蛋白石,产金矿体)→明矾石化带(明矾石 + 石英 ± 地开石 ± 绢云母,产铜矿体)→地开石化带(地开石 + 石英 ± 绢云母)→绢英岩化带(绢云母 + 石英)。金矿与硅化关系极为密切,而铜矿与明矾石化关系密切 [
因紫金山金铜矿床与硅化、明矾石化关系密切,本次研究选择紫金山金铜矿床海拔580 m、568 m、556 m、560 m、676 m的露天采矿平台采集了14件石英和2件明矾石流体包裹体样品,在室内磨制成流体包裹体薄片,然后在显微镜下岩相学观察的基础上,开展流体包裹体均一温度和冰点温度的测量工作。
流体包裹体岩相学观察及显微测温在福州大学紫金地质与矿业学院矿产资源研究中心实验室完成。流体包裹体显微测温采用的是英国产THMSG-600 (LINKAM)型冷热台,用液氮进行冷却,测温范围:−196℃~600℃;温度精度和稳定性:0.01℃;光孔直径:1.3 mm;样品X,Y轴向移动:16 mm样品加热直径:22 mm;加热/冷冻速率:0.01~150℃/min。
紫金山金铜矿床下部铜矿体流体包裹体的寄主矿物主要为石英和明矾石。通过显微镜下对石英和明矾石流体包裹体的观察,发现石英中发育大量的流体包裹体,而明矾石中流体包裹体粒度和数量均较少。根据Roedder [
液相包裹体(L型):该类包裹体大部分呈椭圆形、近圆形、不规则形状和负晶形等,直径大小大多数为7~12 μm,少数直径可达到25 μm,气体整体占比5%~30% (图2(a)),升温时均一到液相。
气相包裹体(V型):该类包裹体主要呈椭圆状和次椭圆状,直径大小一般为5~25 μm,气相整体占比70%~90% (图2(c)),升温时均一至气相。
CO2包裹体(C型):C型包裹体是两相CO2+ H2O系统,仅在明矾石样品中有少量分布,具有“双眼皮”结构,呈椭圆形、负晶体或不规则形状,大小一般5~25 μm。大多数CO2相体积为60%~90% (图2(b)),加热后均一化为气体;而少量CO2相小于40%,加热后均一为液体。偶见纯CO2包裹体(PC型) (图2(b)),呈椭圆形形状,直径大小约为7 μm。
含子矿物多相包裹体(S型):是指含子矿物的流体包裹体,由一种或多种子矿物组成,其中子矿物包括透明子矿物(图2(c、d))以及不透明子矿物(图2(e、f)),形状一般呈椭圆形或者负晶形,大小一般为5~20 μm,主要分布于明矾石中。
图2. 紫金山铜矿体流体包裹体显微照片
(a)液相包裹体;(b)具“双眼皮”结构的CO2包裹体;(c、d)含透明子矿物包裹体;(e、f)含不透明子矿物包裹体。缩写:LH2O:H2O液体;VH2O:H2O蒸气;VCO2:CO2蒸气;LCO2:CO2液体;Tr:透明的子矿物;Op:不透明子矿物。
本次研究共测量了538个流体包裹体,获得538个均一温度和冰点温度,测试结果见表1和图3。
气液两相包裹体用冷冻法测温来计算流体包裹体的盐度 [
ω = 0. 00 + 1. 78 t m − 0. 044 2 t m 2 + 0. 000 557 t m 3
式中:ω为盐度,单位%;tm为冰点下降温度,单位℃,即所测冰点的绝对值。
CO2包裹体由所测笼合物熔化温度,利用Roedder [
ω NaCl = 15.52022 − 1.02342 T − 0.05286 T 2
式中:ωNaCl为水溶液中NaCl的质量百分数,T为CO2笼形物的熔化温度(℃),它的应用范围为−9.60℃ ≤ T ≤ + 100℃。
L型:均一温度变化范围为129.87℃~430.14℃,主要温度集中在160℃~220℃和360℃~380℃ (图3(A));盐度范围在0.18% NaCl eqv~16.9% NaCl eqv;平均盐度为4.23% NaCl eqv (图3(B))。
V型:均一温度变化范围为135.74℃~410.44℃,主要温度集中在180℃~220℃和300℃~320℃ (图3(A));盐度范围在2.16% NaCl eqv~13.83% NaCl eqv;平均盐度为5.98% NaCl eqv (图3(B))。
C型:固态CO2的熔化温度介于−60.4℃~−57.4℃,比CO2的三相点要低,说明CO2包裹体中还有其他成分。包裹体均一温度在145.15℃~316.48℃,主要集中在160℃~180℃ (图3(A));盐度范围在0.8% NaCl eqv~14.3% NaCl eqv,平均盐度为7.4% NaCl eqv (图3(B))。
图3. 紫金山铜矿体流体包裹体均一温度直方图(A)和盐度直方图(B)
L——液相包裹体;V——气相包裹体;C——CO2包裹体
矿物 | 样品编号 | 测点数 | 大小/μm | 冰点/℃ | 均一温度/℃ | w (NaCl) (%) | |||
---|---|---|---|---|---|---|---|---|---|
范围 | 均值 | 范围 | 均值 | 范围 | 均值 | ||||
石英 | HL01 | 34 | 3.0~11.7 | −12.3~−0.3 | −4.9 | 130.11~359.15 | 235.71 | 0.53~16.24 | 9.13 |
石英 | HL02 | 40 | 6.0~18.2 | −9.7~−0.2 | −3.3 | 129.87~372.14 | 205.79 | 0.35~13.62 | 5.17 |
石英 | HL04 | 37 | 4.4~11.6 | −6.1~−0.4 | −2.4 | 136.14~385.65 | 258.24 | 0.71~9.34 | 3.94 |
石英 | HL06 | 45 | 4.8~13.4 | −8.7~−0.2 | −2.3 | 139.78~365.21 | 239.19 | 0.35~12.51 | 3.73 |
石英 | HL08 | 31 | 4.3~13.4 | −3.8~−0.1 | −0.9 | 178.15~360.14 | 232.89 | 0.18~6.16 | 1.56 |
石英 | HL10 | 34 | 5.5~11.6 | −4.6~−0.7 | −2.3 | 168.54~278.14 | 217.78 | 1.23~7.31 | 3.86 |
石英 | HL12 | 29 | 4.2~17.3 | −6.3~−0.1 | −1.7 | 145.89~430.14 | 249.48 | 0.18~9.60 | 2.89 |
石英 | HL13 | 34 | 6.1~23.4 | −5.7~−0.3 | −2.6 | 167.54~410.33 | 276.23 | 0.53~8.81 | 4.20 |
石英 | HL14 | 29 | 5.7~12.3 | −9.3~−0.1 | −2.8 | 153.12~401.24 | 279.41 | 0.18~13.07 | 4.78 |
石英 | HL15 | 30 | 4.8~16.7 | −9.2~−0.1 | −3.0 | 143.12~401.25 | 243.31 | 0.18~12.96 | 4.60 |
石英 | HL16 | 33 | 5.2~9.5 | −10.1~−0.2 | −2.7 | 132.15~404.67 | 254.39 | 0.35~14.04 | 4.28 |
明矾石 | HL17 | 31 | 6.3~13.6 | −7.9~−0.1 | −2.7 | 134.25~398.14 | 228.25 | 0.18~11.58 | 4.31 |
石英 | HL18 | 36 | 6.3~13.1 | −10.7~−0.2 | −3.1 | 156.33~368.11 | 224.45 | 0.35~14.67 | 4.99 |
明矾石 | HL19 | 31 | 5.2~12.4 | −10.9~−0.2 | −3.2 | 145.14~415.14 | 231.37 | 0.35~14.87 | 4.89 |
石英 | HL20 | 33 | 5.4~13.8 | −13.0~−0.2 | −3.0 | 142.71~410.44 | 228.19 | 0.35~16.89 | 4.67 |
石英 | HL21 | 33 | 5.8~19.7 | −9.3~−0.2 | −2.4 | 142.22~400.34 | 248.97 | 0.35~13.18 | 3.93 |
表1. 紫金山铜矿体流体包裹体均一温度、盐度测量结果
由于本次研究未测定含子晶的S型包裹体均一温度和盐度数据,前人 [
从图3(A)可以看出,紫金山金铜矿床铜矿体流体包裹体均一温度主要集中在160℃~220℃、360℃~380℃这2个温度区间,具有中低温和高温成矿流体叠加的特点。
陈景河对紫金山金铜矿床各蚀变带流体包裹体均一温度测定,获得温度范围介于100℃~420℃,并具有120℃~140℃、220℃~240℃和380℃~400℃三个温度峰值,认为矿床热液成矿具多期叠加特征 [
从图4中各样品的均一温度直方图中可以看出来,大部分样品中的流体包裹体都经历了2期热液流体活动:早期热液流体包裹体均一温度较高,晚期热液流体包裹体均一温度较低,说明晚期有大气降水的稀释作用,盐度也有降低的趋势。依据不同样品均一温度直方图中相对高温的峰值温度,绘制了矿区约580 m水平面的成矿流体均一温度等值线图(图4),显示该水平面上高温等值线呈NW-SE走向,具有中心温度相对较高两侧温度相对较低、东南部为高温区(未封闭)的特征,暗示成矿热源中心位于矿区东南侧,成矿流体由矿区东南部的高温位置向西北的低温方向运移。
将约580 m水平面的成矿流体均一温度等值线图(图4)逆时针旋转45˚后与Zhong et al [
图4. 紫金山铜矿体约580 m水平面流体包裹体均一温度等温线图
图5. 紫金山铜矿体约580 m水平面流体包裹体均一温度等温线图和沿135˚方向流体包裹体均一温度等温线剖面图(据本次研究及文献 [
1) 紫金山金铜矿床下部铜矿体主成矿阶段流体包裹体有液相包裹体、气相包裹体、CO2包裹体和少量含子矿物多相包裹体共4种类型,成矿流体属于简单的NaCl-H2O溶液体系为主。
2) 流体包裹体显微测温显示,紫金山金铜矿床下部铜矿体的流体包裹体均一温度范围为120.9℃~430.1℃,主要集中在160℃~220℃和360℃~380℃这二个温度区间,具有中高温热液和中低温热液叠加成矿的特点。
3) 根据流体包裹体均一温度中较高温度峰值绘制的流体包裹体均一温度等值线图指示成矿热源来自紫金山金铜矿床的东南侧深部,表明矿区东南侧深部仍具有较好的找矿前景。
对匿名审稿人提出的建设性意见,以及紫金矿业集团紫金山金铜矿床及地质矿产勘查院在样品采集中给予的大力帮助,在此表示衷心感谢。
杨小敏,付一航,黎敦朋. 福建紫金山金铜矿床下部铜矿体流体包裹体均一温度测量及地质意义Homogenization Temperature Measurement of Fluid Inclusions in the Lower Copper Ore Body of Zijinshan Gold-Copper Deposit in Fujian and Its Geological Significance[J]. 地球科学前沿, 2024, 14(04): 358-366. https://doi.org/10.12677/ag.2024.144033
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