金顶超大型铅锌矿床角砾岩分形研究及地质意义

doi:10.13745/j.esf.sf.2020.3.24

摘要/Abstract

摘要：

前人研究提出金顶超大型铅锌矿床发育出了多种角砾岩,其成因与盐底辟作用有关。文章对这些角砾岩进行了分形分析,确定了不同角砾岩的角砾形态分维值D_r和粒径大小分维值D_s,来进一步探讨角砾岩的形成过程。其中,D_r表征形态复杂性,可指示角砾迁移距离长短或后化学作用改造情况,D_s表征角砾破碎情况,指示形成角砾的能量大小。研究表明,金顶矿床中一部分角砾岩为蒸发盐或膏砂近原位底辟、破碎灰岩围岩形成,它们具有较小的D_r和D_s值。与这些角砾岩空间过渡的层状砂质胶结灰岩砾角砾岩(或称层状含灰岩角砾砂岩),为蒸发盐而非水流体携带灰岩角砾流出地表,并进入含水沉积系统后形成,角砾未经历水流体搬运、磨圆,具有较小的D_r和较大的D_s值。另外一部分角砾岩为蒸发盐和砂泥质底辟破碎围岩,并共同迁移了一定距离而形成,但总体未发生长距离的迁移,随后进入地表沉积系统中。上述部分角砾岩还经历了形成后的流体交代溶蚀作用,导致D_r值变大。本研究显示,在盐底辟有关铅锌矿床内,赋矿围岩包含多种由不同底辟过程形成的角砾岩。

关键词: 角砾岩, 分形分析, 形成过程, 金顶

Abstract:

Previous studies have determined that a variety of complex breccias in the Jinding Zn-Pb deposit are genetically related to the salt diapirism. In this paper, breccia fractal analysis is used to determine two fractal dimensions of these breccias: D_r (the morphology of clasts) and D_s (particle size distribution), in order to understand their formation process. D_r indicates the morphological complexity and migration distance of the breccias or the degree of modification of the chemical process. D_s indicates the degree of brecciation and amount of energy that forms the breccias. Small D_r and D_s values imply that some of the breccias in Jinding were formed by diapirs of evaporite and gypsum-sand and near-in-situ brecciation of the host limestone. Bedded limestone-clast-bearing sandstone that is spatially transitional with these breccias have smaller D_r and larger D_s values, suggesting that limestone clasts in the sandstone were transported by evaporite rather than water into detrial sediments in a depositional system on the surface. Other breccias were formed by evaporite-sand-mud diapirs in a process where the breccia clasts were transported a certain distance, but the distance is limited and the clasts were not transported to the surface to enter a depositional system. Some of the breccias mentioned above also experienced post-brecciation fluid alteration and dissolution, resulting in a large D_r value. This study shows that evaporite diapir-related Zn-Pb deposits may contain breccias formed by a variety of diapir processes.

Key words: breccia, fractal analysis, formation process, Jinding

中图分类号:

庄天明, 宋玉财, 侯增谦, 张翀. 金顶超大型铅锌矿床角砾岩分形研究及地质意义[J]. 地学前缘, 2020, 27(2): 320-331.

ZHUANG Tianming, SONG Yucai, HOU Zengqian, ZHANG Chong. Fractal analysis of breccias in the super-large Jinding Pb-Zn deposit and its geological implication[J]. Earth Science Frontiers, 2020, 27(2): 320-331.

图/表 10

图1 滇西兰坪盆地地质简图和主要矿床分布(据文献[46]修改)

Fig.1 Simplified geological map and the distribution of main ore deposits of Lanping Basin in western Yunnan. Modified from [46].

图2 金顶铅锌矿床地质图(据文献[47]修改)

Fig.2 Geological map of Jinding lead-zinc deposit. Modified from [47].

图3 金顶矿区岩相特征及矿体分布示意图(据文献[6]修改)

Fig.3 Lithofacies and distribution of ore bodies in the Jinding deposit. Modified from [6].

图4 用于分形分析的不同角砾岩薄片扫描照片 (a)—JDZ11-45,方解石胶结的灰岩砾角砾岩,角砾岩带I内,北厂;(b)—PZ12-2,方解石胶结的灰岩砾角砾岩,角砾岩带I内,跑马坪;(c)—JDZ11-27,混杂状砂质胶结的灰岩砾角砾岩,角砾岩带I内,北厂;(d)—J9-4-3,层状砂质胶结的灰岩砾角砾岩,角砾岩带Ⅱ内,北厂;(e)—PMP1-6-1,石膏胶结的灰岩砾角砾岩,角砾岩带I内,跑马坪;(f)—JZ12-09,膏泥砂胶结的复成分砾角砾岩,角砾岩带Ⅲ内,北厂;(g)—JDZ11-75,砂质胶结的复成分砾角砾岩,角砾岩带Ⅲ内,北厂;(h)—ZK8887-4C,铁泥质胶结的灰岩砾角砾岩,角砾岩带I内,跑马坪。

Fig.4 Scanned photographs of thin-sections of the different breccias used for fractal analysis

图5 用于分形分析的不同角砾岩光面照片 (a)—JDZ11-23,方解石胶结的灰岩砾角砾岩,北厂;(b)—JDZ11-47,方解石胶结的灰岩砾角砾岩,北厂;(c)—JDZ11-96,方解石胶结的灰岩砾角砾岩,北厂;(d)—ZK8988-1-6,方解石胶结的灰岩砾角砾岩,跑马坪;(e)—JDZ11-87,层状砂质胶结的灰岩砾角砾岩,北厂;(f)—JDZ11-114,层状砂质胶结的灰岩砾角砾岩,北厂;(g)—JDZ11-84,砂质胶结的复成分砾角砾岩,北厂;(h)—JDZ11-90,砂质胶结的复成分砾角砾岩,北厂。

Fig.5 Polished surfaces photographs of the different breccias used for fractal analysis

表1 不同角砾岩(薄片尺度)角砾形态分维值和大小分维值

Table 1 The fractal dimension Dr and Ds of the different breccia(thin-section scale)

样品号	角砾岩类型	形态分维值D_r	大小分维值D_s	样品位置
JD11-45	方解石胶结的灰岩砾角砾岩	1.49	1.89	角砾岩带I,北厂东侧
PZ12-2	方解石胶结的灰岩砾角砾岩	2.08	0.84	角砾岩带I,跑马坪
JDZ11-27	混杂状砂质胶结的灰岩砾角砾岩	0.65	0.88	角砾岩带I,北厂东侧
PMP1-6-1	石膏/硬石膏胶结的灰岩砾角砾岩	0.80	1.30	角砾岩带I,跑马坪
ZK8887-4C	铁泥质胶结的灰岩砾角砾岩	0.69	1.21	角砾岩带I,跑马坪
J9-4-3	层状砂质胶结的灰岩砾角砾岩	0.62	1.45	角砾岩带Ⅱ,北厂西侧
JZ12-09	膏泥砂胶结的复成分砾角砾岩	0.67	1.25	角砾岩带Ⅲ,北厂中部
JDZ11-75	砂质胶结的复成分砾角砾岩	1.01	1.41	角砾岩带Ⅲ,北厂中部

表2 不同角砾岩(光面尺度)角砾大小分维值

Table 2 The fractal dimension Ds of the different breccia size distribution (polished surface)

样品号	角砾岩类型	角砾大小分维值D_s	样品位置
JDZ11-23	方解石胶结的灰岩砾角砾岩	1.20	角砾岩带Ⅰ,北厂东侧
JDZ11-47	方解石胶结的灰岩砾角砾岩	1.26	角砾岩带Ⅰ,北厂东侧
JDZ11-96	方解石胶结的灰岩砾角砾岩	1.47	角砾岩带Ⅰ,北厂东侧
ZK8988-1-6	方解石胶结的灰岩砾角砾岩	1.32	角砾岩带Ⅰ,跑马坪
JDZ11-87	层状砂质胶结的灰岩砾角砾岩	1.70	角砾岩带Ⅱ,北厂西侧
JDZ11-114	层状砂质胶结的灰岩砾角砾岩	1.78	角砾岩带Ⅱ,北厂西侧
JDZ11-84	砂质胶结的复成分砾角砾岩	1.78	角砾岩带Ⅲ,北厂中部
JDZ11-90	砂质胶结的复成分砾角砾岩	2.12	角砾岩带Ⅲ,北厂中部

图6 不同角砾岩(薄片尺度)单个具代表性的角砾形态分形图 A—角砾面积;W—带宽,即角砾的最大卷积直径;Dr—单个角砾的形态分维值。

Fig.6 Fractal diagram of the typical morphology of the different breccias (thin-section scale)

图7 不同角砾岩(薄片)角砾大小分形图 N—角砾数量;R—粒径范围;Ds—角砾大小分布分维值。

Fig.7 Fractal diagram of size distribution of the different breccias (thin-section scale)

图8 不同角砾岩(光面)角砾大小分形图 N—角砾数量;R—粒径范围;Ds—角砾大小分布分维值。

Fig.8 Fractal diagram of size distribution of the different breccias (polished surface scale)

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