Skarn Mineral Characteristics of the Ahetala Copper Deposit and Its Geological Significance
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摘要:
阿合塔拉铜矿位于新疆维吾尔自治区阿合奇县境内，地处中国塔里木板块北缘的南天山造山带，是典型的矽卡岩型矿床。为了查明该矿床矽卡岩矿物的类型以及成矿过程与成矿环境，本文在详细的野外调查和室内显微镜观察的基础上，利用电子探针技术对矿床中主要矽卡岩矿物石榴石、辉石、硅灰石、绿泥石、绿帘石的化学成分进行了详细分析。电子探针分析结果表明，矿床中的石榴石为钙铝榴石、钙铁榴石，辉石为透辉石(Di77.74~95.46)，帘石为绿帘石，绿泥石为铁绿泥石，属于典型交代矽卡岩大类中的钙矽卡岩类型。透辉石的Mn/Fe值介于0.00~0.12之间，指示了矿床的铜矿化。推断出矿床的成矿阶段主要经历了早期矽卡岩、晚期矽卡岩(退化蚀变)、氧化物和早期硫化物阶段。成矿环境总体上经历了由矽卡岩期高温、高氧逸度、中-酸性的弱氧化-还原环境，向石英-硫化物期相对低温、高硫逸度、碱性的还原环境的转变过程。
Abstract:BACKGROUND The Ahetala copper deposit is located in Arheqi County, Xinjiang Uygur Autonomous Region. It is located in the South Tianshan orogenic belt, northern margin of Tarim Basin. The deposit belongs to a typical skarn type deposit.
OBJECTIVES In order to determine the types of skarn minerals, as well as the metallogenic process and environment of the deposit.
METHODS Based on detailed field and indoor microscopic observations, electron probe microanalysis (EPMA) was carried out to determine the chemical composition of skarn minerals in the Ahetala copper deposit. RESULTS: The results showed that the skarn minerals were garnet, pyroxene, wollastonite, chlorite and epidote. The EPMA results showed that garnets were grossular and andradite. Pyroxene was diopside (Di77.74-95.46), chlorite was minnesotaite. The Mn/Fe value of diopside was 0.00-0.12, indicating the copper mineralization of this deposit.
CONCLUSIONS The skarn of the Ahetala copper deposit is a typical calcium skarn of metasomatic skarn. According to the mineral paragenetic association and metasomatism, the mineralization stages of the deposit can be divided into early skarn stage, late skarn stage (retrograde alteration), oxide stage and early sulfide stage. From the skarn period to the quartz-sulfide period, the metallogenic environment generally underwent changes from the high temperature, high oxygen fugacity, intermediate-acidic, weak oxidizing-weak reducing environment, to the low temperature, high sulfur fugacity, alkaline reducing environment.
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表 1 辉石电子探针分析数据
Table 1. Electron probe microanalysis data of pyroxene
组分 含量(wB/%) AHTL-005 AHTL-012D AHTL-B5 AHTL-B5B AHTL-B6 SiO2 50.66 52.36 51.98 51.85 53.75 TiO2 0.64 - 0.21 0.13 0.18 Al2O3 2.83 2.75 0.23 0.49 0.03 Cr2O3 0.25 0.14 0.11 - 0.07 TFeO 5.76 3.94 8.45 8.77 3.60 MnO 0.32 - 0.89 0.50 0.43 MgO 14.67 17.31 12.87 12.74 15.81 CaO 23.88 22.30 24.77 24.67 25.49 Na2O 0.68 0.10 0.27 0.27 0.15 K2O - 0.29 - - 0.01 Σ 99.69 99.19 99.78 99.42 99.52 以6个氧原子为基准计算的阳离子数 Si 1.89 1.93 1.97 1.97 1.99 AlⅣ 0.11 0.07 0.01 0.00 0.01 AlⅥ 0.01 0.05 0.00 0.00 0.00 Ti 0.02 0.00 0.01 0.00 0.01 Cr 0.01 0.00 0.00 0.00 0.00 Fe3+ 0.15 0.06 0.09 0.09 0.04 Fe2+ 0.03 0.06 0.17 0.19 0.07 Mn 0.01 0.00 0.03 0.02 0.01 Mg 0.82 0.95 0.73 0.72 0.87 Ca 0.95 0.88 1.00 1.00 1.01 Na 0.05 0.01 0.02 0.02 0.01 K 0.00 0.01 0.00 0.00 0.00 端元组分(%) Wo 47.56 44.94 49.13 49.27 50.08 En 40.65 48.53 35.52 35.40 43.22 Fs 9.35 6.16 14.38 14.36 6.17 Di 95.46 94.42 78.26 77.74 90.79 Hd 3.35 5.58 18.66 20.53 7.81 Jo 1.18 0.00 3.07 1.73 1.40 注：端元组分由Geokit软件计算得出，“-”表示实验结果未达到检测线。Wo—硅灰石；En—顽火辉石；Fs—斜方铁辉石；Di—透辉石；Hd—钙铁辉石；Jo—锰钙辉石。 
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表 2 硅灰石电子探针分析数据
Table 2. Electron probe microanalysis data of wollastonite
组分 含量(wB/%) AHTL-Wo1 AHTL-Wo2 AHTL-Wo3 AHTL-Wo4 AHTL-Wo5 SiO2 50.22 50.48 50.98 50.59 50.42 TiO2 0.17 0.20 0.06 0.02 0.16 Al2O3 0.05 0.03 - 0.01 - Cr2O3 0.14 0.13 0.18 0.24 0.14 TFeO - 0.03 - - 0.06 MnO 0.01 0.06 - - - MgO - 0.12 - 0.04 - CaO 48.92 48.57 48.60 48.95 49.03 Na2O 0.23 0.13 0.26 0.14 0.15 K2O - - - - - Σ 99.74 99.75 100.08 99.99 99.96 以6个氧原子为基准计算的阳离子数 Si 1.96 1.97 1.98 1.97 1.96 AlⅣ 0.01 0.01 0.00 0.00 0.00 AlⅥ 0.00 0.00 0.00 0.00 0.00 Ti 0.01 0.01 0.00 0.00 0.00 Cr 0.00 0.00 0.01 0.01 0.00 Fe3+ 0.11 0.08 0.08 0.09 0.10 Fe2+ 0.00 0.00 0.00 0.00 0.00 Mn 0.00 0.00 0.00 0.00 0.00 Mg 0.00 0.01 0.00 0.00 0.00 Ca 2.05 2.03 2.02 2.04 2.05 Na 0.02 0.01 0.02 0.01 0.01 K 0.00 0.00 0.00 0.00 0.00 端元组分(%) Wo 99.14 99.04 99.04 99.37 99.36 En 0.00 0.34 0.00 0.11 0.00 Fs 0.02 0.14 0.00 0.00 0.09 Ac 0.84 0.48 0.96 0.51 0.55 注：端元组分由Geokit软件计算得出，“-”表示实验结果未达到检测线。Wo—硅灰石；En—顽火辉石；Fs—斜方铁辉石; Ac—阳起石。
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表 3 绿泥石电子探针分析数据
Table 3. Electron probe microanalysis data of chlorite
组分 含量(w/%) AHTL-Chl1 AHTL-Chl2 AHTL-Chl3 AHTL-Chl4 AHTL-Chl5 SiO2 26.39 26.06 25.82 25.62 25.36 Al2O3 19.63 19.96 20.00 20.14 19.93 Cr2O3 0.37 0.23 0.28 0.08 0.05 TFeO 24.34 26.99 27.80 27.60 27.55 MnO 0.20 0.35 0.37 0.36 0.41 MgO 15.91 13.62 13.43 13.16 13.05 P2O5 0.07 0.07 0.14 0.02 0.18 CaO 0.06 0.05 0.11 0.07 0.13 Na2O 0.41 0.37 0.30 0.26 0.23 Σ 87.54 87.93 88.26 87.64 87.07
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表 4 绿帘石电子探针分析数据
Table 4. Electron probe microanalysis data of epidote
组分 含量(w/%) AHTL-Ep1 AHTL-Ep2 AHTL-Ep3 AHTL-Ep4 AHTL-Ep5 Si2O 37.87 38.05 37.84 37.69 38.14 TiO2 - 0.13 - - 0.07 Al2O3 18.42 18.28 18.07 18.57 18.31 Cr2O3 0.17 - 0.07 0.11 0.03 TFeO 17.14 16.46 17.16 16.84 16.57 MnO 0.26 0.12 0.11 0.43 0.11 MgO - - 0.08 - 0.02 CaO 22.58 23.32 23.15 22.62 23.14 Na2O 0.12 0.10 0.07 0.05 0.09 K2O - 0.03 0.02 0.03 - Σ 96.56 96.49 96.57 96.34 96.48 注：“-”表示实验结果未达到检测线。
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