The application of near-infrared spectroscopy to identify altered minerals and its implications for geologic prospecting: A case study of the Gangcha gold deposit in Gansu Province
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摘要:
甘肃岗岔金矿位于秦岭造山带之碌曲-成县逆冲推覆构造带的西段北侧,是典型的构造蚀变岩型金矿床,目前储量可达中型。在矿区地质填图的基础上,采用BJKF-1型近红外矿物分析仪对矿区7号勘探线ZK07-4钻孔、8号勘探线ZK08-6钻孔及27号勘探线的ZK27-1、ZK27-3、ZK27-4钻孔岩心进行蚀变特征研究,识别出的主要蚀变矿物为伊利石、云母类、地开石、高岭石等。蚀变矿物分布及含量变化特点表明,与矿化有关的蚀变主要是绢英岩化,其中已探明矿体多位于采用近红外分析技术圈出的绢英岩化带内。此外,伊利石反射光谱特征参数计算结果表明,伊利石结晶度和Al-OH特征吸收峰形态呈现有规律的变化,即含矿段和近矿段伊利石结晶度大(SWIR-IC值5.5~5.7),Al-OH吸收峰尖锐;远矿段和无矿段伊利石结晶度小(SWIR-IC值1.3~1.5),Al-OH吸收峰平缓,显示含矿段伊利石形成温度较高。上述结果表明,矿区内绢英岩化蚀变及伊利石结晶度、Al-OH峰形是有利找矿标志,对找矿具有实际指导意义。
Abstract:Located on the northwestern side of Luqu-Chengxian thrust nappe zone in Qinling orogenic zone, the Gangcha gold deposit is a classical fractural alteration type gold deposit, in which the reserves of metal gold is up to medium scale. On the basis of geological mapping of the mining area, a BJKF-1 near-infrared mineral analyzer was used for drill hole ZK07-4 along No. 7 exploration line, drill hole ZK08-6 along No. 8 exploration line, and drill holes ZK27-1, ZK27-3, ZK27-4 along No. 27 exploration line to study the alteration characteristics. Some major alteration minerals were identified by the analyzer, which included illite, mica, dickite, kaolinite etc. According to the distribution and content changes of alteration minerals, phyllic alteration is related to mineralization, and the proven orebodies are mainly located in the phyllic alteration zone. Besides, a study of illite spectral reflectance parameters shows that illite crystallinity and Al-OH characteristic absorption peak patterns change regularly, that is to say that the ore part's illite crystallinity is large (5.5~5.7), the absorption peak of Al-OH is sharp, the surrounding rock's illite crystallinity is small (1.3~1.5), and the absorption peak of Al-OH is flat, suggesting that the ore-bearing part's illite was formed at high temperature. These results suggest that phyllic alteration, illite crystallinity and Al-OH profile can be taken as the indicator of mineralization during mineral exploration.
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甘肃惠天然矿业公司在野外工作过程中给予热心帮助，中国地质大学（北京）董国臣教授对本文进行修改，修连存研究员、薄海军硕士、鲍林硕士在论文撰写过程中给予帮助，在此一并表示感谢。
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图 2 岗岔矿区地质图
1—第四系冲洪积层；2—下二叠统大关山组；3—下三叠统隆务河组；4—印支期岩体；5—金矿脉及编号；6—实测断层；7—勘探线及钻孔
Figure 2. Geological map of the Gangcha mining area
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图 3 BJKF-1 识别主要蚀变矿物相对含量
Figure 3. The relative content table of major alteration minerals identified by BJKF-1
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图 4 第27 勘探线云母类矿物相对含量等值线图
Figure 4. Distribution isograms of mica group along No. 27 exploration line
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图 5 第7 勘探线ZK07-4 蚀变矿物分布
Figure 5. Distribution of alteration minerals in drill hole ZK07-4 along No. 7 exploration line
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图 6 第8 勘探线ZK08-6 蚀变矿物分布
Figure 6. Distribution of alteration minerals in drill hole ZK08-6 along No. 8 exploration line
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图 7 第27 勘探线伊利石相对含量等值线图
Figure 7. Distribution isograms of illite along No. 27 exploration line
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图 8 第27 勘探线地开石相对含量等值线图
Figure 8. Distribution isograms of dickite along No. 27 exploration line
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图 9 第27 勘探线高岭石相对含量等值线图
中文注解
Figure 9. Distribution isograms of kaolinite along No. 27 exploration line
英文注解
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图 10 第27 号勘探线蚀变矿物分带
1—高岭石-地开石化带；2—绢英岩化带；3—矿体
Figure 10. Zoning map of the alteration minerals along No. 27 exploration line
表 1 伊利石Al-OH 特征峰分析取样位置
Table 1 List of the locations of illite Al-OH characteristic peak analysis
钻孔 ZK08-6 ZK07-4 ZK07-4 ZK27-1 ZK27-3 ZK27-4 矿脉 2 号脉 2 号脉 3 号脉 5 号脉 5 号脉 5 号脉 海拔高度/m 3191.6 3154.9 2948.9 2970 2699.7 2925.4 3189.6 3148.9 2936.9 2961 2697.7 2921.4 3183.6 3142.9 2931.9 2936 2695.7 2919.4 3181.6 3136.9 2920.9 2926 2691.7 2911.4 3179.6 3130.9 2913.9 2914 2689.7 2899.4 3177.6 3124.9 2909.9 2912 2687.7 2897.4 3176.6 3116.9 2907 3174.6 3110.9 2903 3172.6 2975.9 2902 3169.6 2956.9 2897 
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表 2 ZK07-4 Au-2号脉样品伊利石SWIR-IC 及A 值计算结果
Table 2 Calculations of illite’s SWIR-IC & A from drill hole ZK07-4 gold vein Au-2
编号 海拔高度/m 金品位/10-6 SWIR-IC A值（峰高/半峰宽） 1 3154.9 0.05 1.4036 5.0746 2 3148.9 0.05 1.4036 5.1105 3 3142.9 0.4 1.4042 5.1183 4 3136.9 3.3 5.5370 11.6783 5 3130.9 0.05 1.4046 5.0824 6 3124.9 0.05 1.4047 5.1157 7 3116.9 0.3 5.5296 11.4945 8 3110.9 0.05 1.4044 5.1156
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表 3 ZK08-6 Au-2 号脉样品伊利石SWIR-IC 及A 值计算结果
Table 3 Calculations of illite’s SWIR-IC & A from drill hole ZK08-6 gold vein Au-2
编号 海拔高度/m 金品位/10-6 SWIR-IC A值（峰高/半峰宽） 1 3191.6 0.05 1.4040 5.1107 2 3189.6 0.05 1.3476 3.2559 3 3183.6 1.78 5.5619 11.5318 4 3181.6 0.05 1.4038 5.3288 5 3179.6 0.05 1.4047 4.7813 6 3177.6 0.05 6.8503 3.1588 7 3176.6 1.30 5.5420 11.6148 8 3174.6 0.89 5.5393 11.4752 9 3172.6 0.78 5.5406 11.4132 10 3169.6 0.05 1.4041 5.1209
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表 4 ZK07-4 Au-3 号脉样品伊利石 SWIR-IC 及A 值计算结果
Table 4 Calculations of illite’s SWIR-IC & A from drill hole ZK07-4 gold vein Au-3
编号 海拔高度/m 金品位/10-6 SWIR-IC A值（峰高/半峰宽） 1 2948.9 0.78 5.5441 11.5766 2 2936.9 0.86 5.5414 11.5482 3 2931.9 0.05 5.5319 11.5107 4 2920.9 3.18 5.5399 11.4767 5 2913.9 0.05 1.4041 5.3590 6 2909.9 0.05 1.4042 5.0905 7 2948.9 0.35 5.5461 11.5277 8 2936.9 0.55 5.5509 11.4524 9 2931.9 0.73 5.5411 11.6234
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表 5 ZK27-4 Au-5 号脉样品伊利石SWIR-IC 及A 值计算结果
Table 5 Calculations of illite’s SWIR-IC & A from drill hole ZK07-4 gold vein Au-5
编号 海拔高度/m 金品位/10-6 SWIR-IC A值（峰高/半峰宽） 2925.4 0.05 1.4029 5.1060 2 2921.4 0.05 1.4037 4.9854 3 2919.4 0.05 1.4035 5.0521 4 2911.4 1.07 5.5529 11.3363 5 2899.4 0.05 1.4042 5.0272 6 2897.4 0.05 1.4040 5.0545
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表 6 ZK27-3 Au-5 号脉样品伊利石SWIR-IC 及A 值计算结果
Table 6 Calculations of illite’s SWIR-IC & A from drill hole ZK27-3 gold vein Au-5
编号 海拔高度/m 金品位/10-6 SWIR-IC 均值 A值（峰高/半峰宽) 均值 1 2699.7 0.05 1.4048 1.40478 5.0746 5.0746 2-1 2697.7 5.5378 11.2295 2-2 2697.7 0.05 5.5354 4.1593 11.8795 9.3424 2-3 2697.7 1.4047 4.9182 3 2695.7 1.33 5.5432 5.5433 11.5401 11.540 4-1 2691.7 5.5545 11.2570 4-2 2691.7 0.05 1.4049 4.1689 5.1774 9.2743 4-3 2691.7 5.5474 11.3886 5 2689.7 0.05 1.4043 1.4043 5.0602 5.0602 6 2687.7 0.05 1.4048 1.4048 5.0394 5.0394
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表 7 ZK27-3 Au-5 号脉样品伊利石SWIR-IC 及A 值计算结果
Table 7 Calculations of illite’s SWIR-IC & A from drill hole ZK27-3 gold vein Au-5
编号 海拔高度/m 金品位/10-6 SWIR-IC 均值 A值（峰高/半峰宽) 均值 1 2699.7 0.05 1.4048 1.40478 5.0746 5.0746 2-1 2697.7 5.5378 11.2295 2-2 2697.7 0.05 5.5354 4.1593 11.8795 9.3424 2-3 2697.7 1.4047 4.9182 3 2695.7 1.33 5.5432 5.5433 11.5401 11.5401 4-1 2691.7 5.5545 11.2570 4-2 2691.7 0.05 1.4049 4.1689 5.1774 9.2743 4-3 2691.7 5.5474 11.3886 5 2689.7 0.05 1.4043 1.4043 5.0602 5.0602 6 2687.7 0.05 1.4048 1.4048 5.0394 5.0394
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