安徽金寨沙坪沟矿区地应力测量与现今应力场研究

安徽金寨沙坪沟钼矿位于秦岭—大别山成矿带东段,是近年来我国发现的世界级特大钼矿,其开采设计和地质安全评价备受重视。为了查明沙坪沟矿区现今应力场特征,指导矿区开采设计,在矿区3个700~1000 m深钻孔中开展了水压致裂法地应力测量工作,测量结果表明:(a)矿区最大、最小水平主应力随深度增加梯度系数分别为0.0226和0.0166,与区域地应力背景值基本一致;(b)矿区实测最大水平主应力优势方位为NE-NEE向,与区域构造应力场方向一致;(c)实测地应力数据揭示的应力结构与区域结果存在差异,分析认为,沙坪沟矿区所在的桐柏—大别构造带特殊的构造位置和构造活动机制可能是造成这种差异的主要原因。进一步,利用库伦滑动摩擦准则评价了实测地应力数据,探讨了其对矿区开采设计的意义,结果表明,矿区现今地应力强度不足以导致以断裂失稳活动或地震为表现形式的地应力状态调整事件的发生,从地应力角度讲,沙坪沟矿区目前总体处于稳定的构造应力环境。本文结果,对于沙坪沟矿区开采设计、地质安全评价及大别山造山带东段构造应力场研究有重要意义。

Estimation on In-situ Stress Measurements and Present-day Stress Field in the Shapinggou Molybdenum Deposit, Jinzhai County, Anhui Province

The Shapinggou molybdenum deposit located in the East Qinling-Dabie metallogenic belt is a superlarge porphyry molybdenum deposit discovered in recent years. Much attention has been paid to the exploitation designing and geological safety evaluation of this deposit. To thoroughly understand the present-day stress field in the Shapinggou molybdenum deposit and put forward suggestions for the exploitation designing, the authors conducted in-situ stress measurement using hydraulic fracturing method in three drill holes at the depths of 700~1000 m in the Shapinggou molybdenum ore district. The measurement results reveal that the grade coefficients of the maximum, minimum horizontal principal stresses versus depths are 0.0226 and 0.0166, respectively, which are consistent with previous results representing the regional tectonic stress field. The measured in-situ stress data also indicate that the dominant direction of the maximum horizontal stress in the Shapinggou molybdenum ore district is in NE?NEE direction, which is consistent with the regional tectonic stress field. However, the stress regimes inferred from the measured in-situ stress data are not consistent with regional results inferred from other methods. The unique tectonic location and the tectonic evolution mechanism of the Tongbai-Dabie tectonic belt where the Shapinggou molybdenum deposit occurs are considered to be the main factors inducing the discrepancy between the Shapinggou molybdenum deposit and the regional results. Furthermore, the measured in-situ stress data and their implications for the exploitation designing of the Shapinggou molybdenum deposit were estimated by using the Column frictional failure criterion. It is noted that the measured in-situ stress levels in the ore district are lower than those expected to induce the stress field adjustment in the form of fault slipping or earthquake, and thus the Shapinggou molybdenum deposit can be considered to be in the relatively stable tectonic stress state now. The results achieved in this study will contribute to exploitation of the Shapinggou molybdenum deposit and geological safety evaluation as well as to the study of tectonic stress field of the Dabieshan orogenic belt.