The genesis of the Chedu gold deposit in Nansha River area, Shaanxi Province
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摘要:
针对陕西南沙河地区车渡金矿床进行了研究，研究结果表明，中-新元古界碧口群二亚群（Pt2-3bk2）中玄武质火山凝灰岩具Sr、Ba、Rb、Ce、P、Sm相对富集，Ta、Nb、Zr、Hf、Ti相对亏损的特征，显示钙碱性火山弧玄武岩的特点；车渡金矿床具有2种成因类型，一是与中生代逆冲推覆构造形成的韧性剪切带有关的强硅化蚀变岩型金矿，二是与中-新元古界碧口岩群二亚群火山凝灰岩有关的BIF型金矿。单颗粒磁铁矿成分分析认为，车渡含金磁铁石英岩中磁铁矿具有高的TFeO（平均值99.59%）含量和极低的TiO2、MgO、A12O3、MnO含量，指示车渡磁铁石英岩金矿石中条带状磁铁矿属于沉积变质型成因条带状含铁建造。含金磁铁石英岩型金矿石的氢氧同位素显示，δ18O水值为12.34‰~12.45‰（平均值12.40‰），δD值为-112.6‰~-103.5‰（平均值-108.05‰），与鞍山-本溪地区条带状含铁建造型铁矿δD变化范围（-129‰~-75‰）一致，暗示车渡含金磁铁石英岩中石英矿物具有条带状含铁建造特征。
Abstract:In this paper, the research work of the Proterozoic deposit in Nansha River area of Shaanxi Province was carried out, and the results show that the basalt volcanic tuff in Bikou Group 2nd sub-group (Pt2-3bk2) is relatively rich in Sr, Ba, Rb, Ce, P and Sm, and depleted in Ta, Nb, Zr, Hf and Ti, exhibiting characteristics of calcium-alkaline volcanic arc basalt. There are two genetic types of the Proterozoic deposits, one is the strongly silicified rock type gold deposits related to the ductile shear zone formed by the Mesozoic thrust Nappe structure, and the other is the BIF type gold deposits related to the 2nd subgroup volcanic tuff of the Meso-Neo Proterozoic period. According to composition analysis of single granular magnetite, the authors hold that magnetite has high TFeO (99.59% on average) content and very low TiO2, MgO, A12O3 and MnO content in gold magnetic quartz, which indicates that the banded magnetite in the Chedu magnetite quartzite gold ore is of sedimentary metamorphic type, i.e., belonging to quartzite type gold deposit. Hydrogen and oxygen isotope features of gold-bearing magnetite quartzite type gold ore show that δ18O water value is 12.34‰~12.45‰ (12.4‰ on average), and δD value is -112.6‰~-103.5‰ (-108.05‰ on average), consistent with BIF variation range of δD-type iron ore in Anshan-Benxi area (-129‰~-75‰), suggesting that quartz minerals in quartz rocks with gold magnetite have BIF characteristics.
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表 1 车渡金矿体特征
Table 1. List of characteristics of the Chedu gold deposit
矿体编号 赋矿岩石 矿体规模 矿体产状 平均品位/(g.t-1) 蚀变组合 控制长/m 平均厚/m 控制斜深/m 倾向/° 倾角/° AuⅠ-1-1 磁铁石英岩 720 1.59 90 350~15 43~72 6.14 褐（黄）铁矿化、磁铁矿化、孔雀石化、碳酸盐化 AuⅠ-1-2 磁铁石英岩 280 0.82 53 0~15 66~73 1.75 弱褐(黄)铁矿磁化、铁矿化、碳酸盐化 AuⅠ-1-3 磁铁石英岩岩 1400 1.35 30 320~350 66~73 3.14 褐（黄）铁矿磁化、铁矿化、碳酸盐化 AuⅠ-2 磁铁石英岩 1200 1.23 88 350~15 40~71 2.58 褐（黄）铁矿磁化、铁矿化、碳酸盐化 AuⅡ-1 强硅化蚀变岩 160 1.75 40 352 83 1.97 硅化、褐铁矿化、黄铁矿化 AuⅡ-2 强硅化蚀变岩 400 0.84 40 352 83 1.68 硅化、褐铁矿化、黄铁矿化、弱磁铁矿化 
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表 2 车渡金矿岩石样品主量、微量和稀土元素含量
Table 2. Major, trace and rare earth elements of samples in the Chedu gold deposit
样品号 SiO2 Al2O3 TFe2O3 K2O Na2O MgO MnO CaO TiO2 P2O5 SO3 烧失量 Ba Hf Nb Rb Sr Ta Th U Zr Y La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu CD301-1 45.17 13.27 14.98 0.31 3.57 3.59 0.19 6.2 3.78 0.4 〈0.01 8.06 138 3.62 2.84 8.32 21 0.15 0.7 0.23 33.4 13.4 7.78 17 2.67 10.1 2.8 0.62 2.45 0.4 2.85 0.49 1.45 0.19 1.74 0.27 CD301-5 48.15 13.77 11.34 0.26 4.04 5.51 0.21 6.62 1.01 0.08 0.5 8.16 61.1 1.87 1.03 3.73 22.3 0.1 0.25 0.23 13.9 12.6 4.91 9.66 1.62 5.6 1.75 0.36 1.57 0.26 2.15 0.41 1.31 0.19 1.75 0.28 CD1-7 84.97 1.95 4.86 0.25 0.24 0.56 0.21 3.52 0.13 0.03 < 0.01 3.4 83.3 13.2 23 5.34 111 1.04 1.18 0.49 214 30.9 20.7 46.8 6.65 31.6 8.15 2.52 8 1.37 7.74 1.42 3.72 0.46 2.64 0.36 CD1-1 53.41 0.9 41.99 0.16 0.01 0.24 0.57 0.69 0.03 0.41 < 0.01 0.93 28.8 2.41 4.99 8.28 46.6 0.36 0.28 0.26 54.1 17.9 3.9 9.2 1.46 7.83 2.56 0.83 2.91 0.61 3.97 0.82 2.47 0.34 2.13 0.3 注：CD301-1、CD301-5为玄武质火山凝灰岩样品，CD1-7、CD1-1为磁铁石英岩金矿石样品。主量元素含量单位为%，微量和稀土元素含量单位为10-6
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表 3 车渡金矿磁铁石英岩中石英单矿物氢氧同位素值
Table 3. The hydrogen and oxygen isotope values of quartz single mineral in magnetite quartz rock of the Chedu gold deposit
岩石 单矿物 δD/‰ δ18O石英/‰ 温度/℃ δ18O水‰ 磁铁石英岩 石英 -112.6 16.6 396 12.45 磁铁石英岩 石英 -103.5 16.4 400 12.34 注：δ18O水=δ18O石英-1000lnαQ-W, 1000lnαQ-W =3.38×106T-2-3.4[18]
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