自然重砂成因矿物学特征及找矿指示作用

doi:10.13745/j.esf.sf.2020.5.46

摘要/Abstract

摘要：

自然重砂是地质体经自然风化、剥蚀、搬运、沉积等地质作用而分离出的单矿物(或矿物组合)。自然重砂矿物晶体由于仍然保留有许多矿物成因信息,包括颜色、形态、化学成分、物理性质和矿物组合等特征,因此常用于追溯源区地质体或者找矿勘查。这种方法被认为是一种经济实用的找矿方法——自然重砂测量。本文基于全国自然重砂找矿的数据资料,系统梳理了自然重砂的矿物类型、出现频率及其分布等特点,分析了自然重砂的矿物组合和成因矿物学特征,研究了自然重砂矿物的源区烙印、搬运距离及标型指示矿物组合特征,探讨了自然重砂成因矿物学研究意义及其找矿应用前景。自然重砂矿物的颜色、形态及内部结构依然保留着明确的成因矿物学信息:其颜色和晶体形态具有继承性而与其源区母体联系起来,体现源区母体的特性;其矿物组成可分出残余原生重矿物(包括造岩矿物、副矿物、矿石矿物等)和新生重砂矿物两个部分,如赤铜矿、孔雀石等反映着源区岩性体的成分或者赋存状态特征,其矿物组合也在很大程度上继承原生共生矿物而体现诸如有无矿化等意义;重砂颗粒的磨圆度、边界光滑性等表面特征反映搬运距离,有利于明确响应源区母体或者物源,而具有良好的找矿指示意义。

关键词: 自然重砂, 成因矿物学, 找矿方法, 应用, 前景分析

Abstract:

Heavy mineral placers are naturally detached mineral grains (or mineral association) produced by natural weathering, erosion, transportation and deposition processes. Because heavy mineral placers can preserve large amount of genetic information on minerals, such as color, morphology, chemical composition, physical feature and mineral association, it can be utilized for back tracing the original ore bodies or for mineral exploration. Hence an easy and simple method, called natural heavy mineral placer survey, for ore exploration is gradually developed. In this article, based on the survey data, we summarized the mineral types, occurring frequency and distribution characteristics of heavy mineral placers, studied mineral association features of the heavy placers and their genetic mineralogical characteristics, and analyzed the relict of the original ore body, possible transporting distances and typomorphic indicating mineral association. We also discussed the significance in ore prospecting potential when genetic mineral characteristics of natural heavy mineral placer are used. The color, morphology and texture of heavy mineral placer still clearly retain the original typomorphic information as they are inheritable factors corresponding closely to the characteristics of the source host rocks. The placer minerals can be divided into two parts: the residual original heavy minerals including common silica, access and ore minerals, and the newly formed ones during erosion and transportation, including cuprite and malachite, reflecting both the lithology in the source area and the present formation condition. The placer mineral association is mostly inherited from primitive paragenetic mineral assemblages, therefore it can provide information on the mineralization potential. The grain features such as roundness and boundary smoothness reflect placer transport distance, they are favorable properties for identifying the responsible host rocks in the source area to guide mineral exploration.

Key words: natural mineral placer, genetic mineralogy, ore exploration method, application, prospect analysis

中图分类号:

董国臣, 李胜荣, 申俊峰, 董朋生, 李华伟, 殷国栋, 汤家辉. 自然重砂成因矿物学特征及找矿指示作用[J]. 地学前缘, 2020, 27(5): 171-178.

DONG Guochen, LI Shengrong, SHEN Junfeng, DONG Pengsheng, LI Huawei, YIN Guodong, TANG Jiahui. Genetic mineralogy of natural heavy placer minerals and its effectiveness in mineral prospecting[J]. Earth Science Frontiers, 2020, 27(5): 171-178.

图/表 6

表1 中国自然重砂矿物及其产出频数[2]

Table 1 Glossary of natural heavy placer minerals and production frequencies in China[2]

重砂矿物	频数/件	重砂矿物	频数/件	重砂矿物	频数/件
矿石矿物		雌黄	4 954	硅线石	33 967
自然金	106 869	雄黄	85 179	十字石	50 311
黄铁矿	769 246	标志矿物		尖晶石	45 205
黄铜矿	49 185	铬铁矿	245 374	金红石	1 321 484
自然铜	8 980	磁铬铁矿	10 028	蓝晶石	55 263
磁铁矿	669 218	铬尖晶石	101 186	黄玉	15 582
赤铁矿	452 844	镁铝榴石	308	褐帘石	98 328
褐铁矿	470 986	镁钛铁矿	260	绿帘石	683 601
方铅矿	94 663	镁铁尖晶石	2 021	锡石	248 576
白铅矿	121 056	铁尖晶石	998	毒砂	28 758
黄钾铁钒	18 427	铁金红石	1 520	辰砂	326 974
黑钨矿	64 912	钛铁矿	1 200 972	阳起石	10 604
白钨矿	490 519	板钛矿	181 315	叶蜡石	579
辉钼矿	10 356	锐钛矿	856 254	萤石	26 940
辉锑矿	2 073	(钛)磁铁矿	58 092	重晶石	537 664
钨铅矿	13 737	副矿物		石膏	6 251
自然铅	40 406	锆石	1 725 483	造岩矿物
胶磷矿	431 049	石榴子石	886 529	橄榄石	21 836
磷氯铅矿	28 685	白榴石	416	辉石	348 334
磷钇矿	106 533	榍石	471 311	紫苏辉石	6 142
钼铅矿	40 207	磷灰石	235 246	透辉石	41 605
钍石	146 463	电气石	876 192	透闪石	56 346
软锰矿	75 180	独居石	713 937	角闪石	470 307
硬锰矿	74 572	红柱石	25 200

图1 自然重砂矿物总量(a)和频数(b)比例图 a—数量;b—出现频数。上述分析可以看出,占重砂15%左右重砂矿物,作为极稳定矿物,占据了出现频数的60%以上,并在自然重砂中起着主要作用。(3)自然重砂具有区域性分布趋势.据全国矿产资源潜力评价自然重砂数据汇总与编图结果[2,7]分析,检出率较高的85个矿物具有明显的区域性趋势。部分重砂矿物如锆石、铬尖晶石、铬铁矿、硅线石、褐帘石、红柱石、辉钼矿、辉石、尖晶石、蓝晶石等,更易发育在造山带。在稳定的构造区如华北克拉通、秦祁昆造山带及中亚造山带等也常发育一些特征的重砂矿物,如硅线石、黑云母、磷灰石、闪石类、榍石[2]。而多数的重砂矿物,如自然金、黄铁矿、黄铜矿、金红石、磁铁矿、锆石、石榴子石等,在不同地区均有分布,主要体现在富集程度差异。(4)一些单元素自然重砂或者单矿物,如自然金、自然铂、磁铁矿、铬铁矿、锡石、金红石、绿柱石等,可以提供更多的矿床学信息,部分可以直接通过自然重砂矿物研究来追索矿床产地。

Fig.1 Occurrence diagrams of the natural heavy placer mineral overall (a) and the production frequencies (b)

图2 重砂矿物的颜色和形态特征 a—滇西来利山地区锡石;b—不同形态的黄铁矿(a) The Lailishan cassiterite from western Yunnan Province; (b) Pyrites of different morphologies.。

Fig.2 Colors and morphologies of mineral placers.

图3 重砂矿物自然金颗粒边缘和表面擦痕特征

Fig.3 Grain margin and surface scratch characteristics of native gold placers

图4 滇西来利山地区重砂锡石变化特征[10]

Fig.4 Variation of cassiterite placer abundance in the Lailishan area,western Yunnan with transport distance (adapted from [10])

表2 夕卡岩型白钨矿重砂分布规律

Table 2 Skarn type wolfmite placer distribution pattern

距离 /km	颗粒量情况		粒度 /mm	颗粒形态
距离 /km	含量/ (g·m^-3)	粒数	粒度 /mm	颗粒形态
<1	>1 000		2~4	四方双锥
1~2	100~500		0.5~1	棱角状
>2~4		>1 000	0.1~0.5	次浑圆状
>4~7		80~150	0.1~0.3	浑圆状
>7		<80	<0.1	浑圆状

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