天山山脉剥露程度与矿产保存关系初探

成矿后含矿地质体的剥露程度与矿体的保存关系是矿床学研究的疑难问题之一.利用中酸性侵入岩体的出露程度, 结合磷灰石裂变径迹测试结果及现今发现的矿产展布特征, 探讨天山山脉剥露程度与内生金属矿产保存之间的关系, 进而为区域找矿提供理论指导.统计结果表明, 北天山西段的依连哈比尕尔山、中段的博格达山和西南天山山脉皆缺乏大面积分布的深成侵入岩, 已经发现的内生金属矿产较少, 且以中低温的矿床为主; 北天山南部的觉罗塔格地区、中天山和南天山东段都大面积出露中酸性岩体, 已经发现了大量大型-超大型规模内生金属矿床, 以中高温成矿为特征; 综合分析已有的磷灰石裂变径迹测年结果统计显示, 北天山西段的依连哈比尕山、中段的博格达山和西南天山中生代晚期开始隆升, 新生代25 Ma以来隆升强烈; 北天山南部、中天山以及南天山东段山脉从侏罗纪早期就已经开始隆升而接受剥蚀, 新生代隆升较弱.结合现今山脉的地质背景、内生金属矿产展布特征、山脉隆升时间及其现今地貌特征推测, 北天山西段的依连哈比尕山、中段的博格达山和西南天山山脉由于剥蚀时间短, 因而其剥蚀程度相对较低, 地表仍出露表壳的沉积-火山岩系, 以中酸性侵入岩体为代表的深成岩体由于剥蚀量不够而还没有出露于地表, 地表出露低温的内生金属矿产; 北天山南部、中天山以及南天山东段山脉开始隆升时间早, 新生代隆升弱, 因而总体上剥蚀量、剥蚀程度大, 表壳岩系已经剥蚀殆尽, 广泛出露深成侵入岩体, 与中酸性岩体侵位有关的中高温矿产广泛展布.为此, 进一步指出了在天山山脉不同构造分区内应该着重寻找不同类型、不同成矿温度的内生金属矿产, 推测西南天山具有较好的找矿远景空间, 并认为山体剥露程度的差异是造成所谓"大矿不过国界"的主要原因之一. 

Exhumation Degree of the Tianshan Range and Its Implications for Ore Preservation

The exhumation of ore-bearing rocks after mineralization plays an important role in the ore preservation, and their relation is one of major issues of mineral deposit geology. The number percentage and area proportion of intermediate-acid intrusive bodies are regarded as two indexes of mountain exhumation degree in this paper. The temperature-space distribution of current outcropped deposits in Tianshan range not only is helpful for understanding the relationship between the mountain exhumation with the preservation of early-formed deposits, but also facilitates further ore-prospecting. Statistics results show that there are very few number and little area proportion of intermediate-acid intrusive bodies in Yilianhabigaer mountain in western segment of north Tianshan, Bogeda mountain in middle segment of north Tianshan, and southwest Tianshan, where there are only few outcropped metal ore deposits mainly characterized by epithermal mineralization. And relative deeply intrusive rocks, as well as lots of large to super-large intrusive-rock-related meso-hypothermal ore deposits, are widely exposed in Jueluotage area in southern part of north Tianshan, middle Tianshan unit, and Kuluketage area in eastern segment of south Tianshan. Previous data from fission track dating of apatite shows that Yilianhabigaer mountain, Bogeda mountain, and southwest Tianshan initially uplifted at the end of the Mesozoic, followed by rapid uplift and deformation since about ca.25 Ma. Mountains in middle Tianshan, southern part of north Tianshan, and eastern segment of south Tianshan begun to uplift rapidly and denudate since the Early Jurassic, but only weak uplift occurred in the Cenozoic. The outcropped rocks, the distribution characteristics of metal ore deposits, and the uplift-exhumation process of mountains suggest that superficial volcano-sedimentary rocks are still preserved in Yilianhabigaer mountain, Bogeda mountain, and southwest Tianshan, because of shallow erosion as response to short-time sustained denudation and rapid uplift during the late Cenozoic, leading to exposure of few intermediate-acid intrusive bodies and mostly epithermal metal deposits at the surface. While those superficial volcano-sedimentary rocks in middle Tianshan, southern part of north Tianshan, and eastern segment of south Tianshan probably have already been denudated away due to long-time erosion since the Middle Mesozoic and weak deformation in the Cenozoic, and deeply intrusive rocks and meso-hypothermal ore deposits widely outcropped at the surface as a result. As to the ore-prospecting in distinct units of Tianshan range, it is suggested that various types of deposits with different ore-forming temperature should be focused on at the surface and there is favorable mineralization potential in southwest Tianshan. It also shows that the exhumation diversity of mountain is one of the most important reasons for the popular saying that "large deposits are limited within the national boundary".