Zircon U-Pb age of intrusive rocks and molybdenite Re-Os age for Lianzigou Au deposit in Xiaoqinling area and its geological significance
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摘要:
镰子沟金矿床位于小秦岭金矿集区西部，矿体受断裂和石英脉体控制，围岩蚀变以钾化和硅化为主。矿床浅部以金矿为主，深部发现金钼（共）伴生矿体。为了确定镰子沟金矿床成岩、成矿时代，选择镰子沟金矿床正长斑岩和金钼矿石分别进行了LA-ICP-MS锆石U-Pb和辉钼矿Re-Os同位素研究。获得正长斑岩的207Pb/206Pb年龄加权平均值为1802.9±9.9Ma，此年龄明显早于小秦岭地区金矿床的形成时代；获得辉钼矿Re-Os等时线年龄为128.8±6.5Ma，指示矿床形成于早白垩世，晚于区域已知花岗岩形成时代。综合研究认为，镰子沟金矿床的形成与区域花岗岩无关，可能与深部流体或隐伏岩浆有关。
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关键词:
- 地质特征 /
- LA-ICP-MS锆石U-Pb年龄 /
- Re-Os年龄 /
- 成岩成矿时代 /
- 镰子沟金矿床
Abstract:The Lianzigou gold deposit is located in the west of Xiaoqinling Au ore concentration area. The orebodies are hosted in the upper strata of Taihua Group and controlled by fault fracture zone or quartz veins. The wall rock alteration is dominated by potassium alteration and silicification. Au (Mo) orebodies have been discovered in the depth of the deposit. To constrain its petrogenic and metallgogenic ages, the authors carried out LA-ICP-MS zircon U-Pb dating on syenite porphyry and Re-Os dating on molybdenite, respectively. LA-ICP-MS zircon U-Pb dating of syenite porphyry gave a weighted average age of 1802.9±9.9Ma, which is clearly older than the age of large-scale gold mineralization in the Xiaoqinling area. Re-Os dating on molybdenite from the Au orebodies gave an isochron age of 128.8±6.5Ma, indicating that the Au and Mo mineralization occurred in Early Cretaceous. The Re-Os age is younger than the petrogenic ages of granites in the Xiaoqinling area, showing that there is no direct relationship between the known granitic magmatism and the mineralization of the Lianzigou Au deposit. Deep fluids or concealed magmatic intrusion probably played an important role in mineralization.
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表 1 镰子沟金矿床正长斑岩LA- ICP-MS锆石U-Th-Pb同位素数据
Table 1. LA- ICP-MS zircon U-Th-Pb isotopic data for syenite-porphyry from the Lianzigou Au deposit
分析点号 Th/10-6 U/10-6 Th/U 同位素比值 年龄/Ma 207Pb/206Pb +1σ 207Pb/235U +1σ 206Pb/238U +1σ 207Pb/206Pb +1σ 207Pb/235U +1σ 206Pb/238U +1σ LZ-20-3 88 114 0.77 0.11033 0.00159 4.7408 0.07512 0.31165 0.00404 1805 13 1774 13 1749 20 LZ-20-6 49 56 0.87 0.11013 0.00375 4.75394 0.16408 0.31309 0.00551 1802 38 1777 2 1756 27 LZ-20-10 118 110 1.08 0.11014 0.00168 4.51894 0.07516 0.29757 0.00388 1802 14 1734 14 1679 19 LZ-20-11 24 31 0.78 0.11036 0.00468 4.799 0.20184 0.31536 0.00623 1805 48 1785 35 1767 31 LZ-20-12 96 345 0.28 0.11027 0.00195 4. 96993 0.09337 0.32686 0.0044 1804 17 1814 16 1823 21 LZ-20-18 23 30 0.76 0.11045 0.00647 4.96918 0.28668 0.32627 0.00828 1807 68 1814 49 1820 10 LZ-20-19 88 143 0.62 0.11027 0.00404 4.85384 0.17904 0.31922 0.00485 1804 45 1794 31 1786 24 LZ-20-20 113 130 0.87 0.11017 0.00154 4.89413 0.07565 0.32216 0.00419 1802 13 1801 13 1800 20 LZ-20-21 2: 45 0.56 0.11004 0.00437 4.83971 0.19082 0.31896 0.00623 1800 44 1792 33 1785 30 LZ-20-23 167 200 0.84 0.1102 0.00125 4.61519 0.06121 0.30373 0.00383 1803 11 1752 11 1710. 19 LZ-20-24 269 283 0.95 0.11013 0.00131 5.04404 0.0692 0.33215 0.00422 1802 11 1827 12 1849 20 LZ-20-4 151 273 0.55 0.14625 0.0017 8.59821 0.11647 0.42639 0.00543 2303 10 2296 12 2289 25 LZ-20-5 93 263 0.35 0.14573 0.00165 8.49724 0.11317 0.42289 0.00536 2296 10 2286 12 2274 24 LZ-20-7 100 267 0.37 0.15914 0.00197 10.33216 0.1462 0.47087 0.00609 2447 11 2465 13 2487 27 LZ-20-14 213 324 0.66 0.15962 0.00209 10.1717 0.15091 0.46215 0.00612 2452 11 2451 14 2449 27 LZ-20-16 259 197 132 0.15983 0.00238 10.08622 0.16535 0.45768 0.00609 2454 13 2443 15 2429 27 LZ-20-17 114 194 0.59 0.15919 0.00189 10.19534 0.14012 0.46448 0.00588 2447 10 2453 13 2459 26 LZ-20-1 130 227 0.57 0.1391 0.00473 6.39143 0.1963 0.33325 0.00487 2216 60 2031 27 1854 24 LZ-20-8 200 184 1.09 0.32585 0.00338 14 3458 0.17879 0.3193 0.00401 3598 9 2773 12 1786 20 LZ-20-9 314 368 0.85 0.18304 0.00481 8.821 0.19457 0.34952 0.00498 2681 44 2320 20 1932 24 LZ-20-15 97 190 0.51 0.14523 0.0046 6.00355 0.16877 0.29981 0.00439 2291 56 1976 24 1690 22 LZ-20-25 35 48 0.73 0.15786 0.00273 6.63535 0.12122 0.30483 0.00428 2433 14 2064 1 1715 21 LZ-20-2 42 66 0.63 0.0839 0.04434 .1.38335 0.72769 0.11958 0.00603 1290 1181 882 310 728 35 LZ-20-13 444 436 1.02 0.04605 0.00656 0.34164 0.04832 0.05381 0.00088 / 259 298 37 338 5 LZ-20-22 43 58 0.64 0.08664 0.00519 2.18226 0.12608 0.18267 0.00291 1353 119 1175 40 1082 16 注“：/”表示无数据 
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表 2 镰子沟金矿床辉钼矿Re-Os同位素测试结果
Table 2. Analytical result of Re-Os isotopes of molybdenites from the Lianzigou Au deposit
样名 矿石类型 样重/g Re/10-9 普Os/10-9 187Re/10-9 187Os/10-9 187Os/普
Os测定值 2 测定值 2 测定值 2 测定值 2 LZ-11 钾长石-石英脉型 0.25 97.11 1.51 0.20 < 0.01 61.04 0.95 0.15 < 0.01 0.78 LZ-12 0.25 390.70 2.48 2.88 0.02 245.56 1.56 0.78 < 0.01 0.27 LZ-13 0.19 173.25 1 66 0.25 < 0.01 108.89 1.04 0.26 < 0.01 1.04 LZ-14 0.25 179.59 1.80 3.77 0.07 112.88 1.13 0.62 < 0.01 0.16 LZ-15 碎裂岩型 0.25 70.41 0.71 2.84 0.04 44.25 0.44 0.39 < 0.01 0.14
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表 3 镰子沟金矿床辉钼矿Re-Os同位素参数及模式年龄
Table 3. Re-Os isotopic parameters and model ages of the molybdenites from the Lianzigou Au deposit
样名 187Re/188Os 187Os/188Os 等时线初始值 模式年龄/Ma 测定值 2σ 测定值 2σ 187Os/188Os 修正后 LZ-11 2399 47.08 5.96 0.11 0.75+0.13 130.19 LZ-12 655 6.87 2.08 0.02 121.25 LZ-13 3388 69.72 8.02 0.18 128.72 LZ-14 229 5.06 1.25 0.03 131.35 LZ-15 119 1.95 1.07 0.02 158.63 注:扣除非放射成因的普Os中187Os计算模式年龄方法见李超等[20]
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