Geophysical response characteristics of the Dapai polymetallic mining area in Southwestern Fujian Province and its prospecting implications
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摘要:
大排多金属矿区位于闽西南坳陷大田—龙岩次级坳陷带南部，政和—大埔深大断裂西侧，是福建省较大的多金属矿产地之一.随着找矿勘查的不断深入，对在该矿区外围和深部寻找隐伏矿床提出了迫切需求，但研究区地表地形崎岖、植被茂密，以往很少进行高精度大比例尺的综合地球物理调查，因此对隐伏的控矿构造、赋矿层位和火成岩体分布的认识远不能满足深部找矿的需求.本文实施了反射地震、可控源音频大地电磁剖面测量和大比例尺航磁面积性测量，在成矿理论和找矿模型的指导下采用反射地震真地表偏移成像技术、可控源音频大地电磁二维带地形反演技术和航磁数据精细处理与三维反演技术，提取识别了剖面浅层逆冲推覆控矿构造和赋矿层位的反射地震特征，与成矿关系密切的燕山期火成岩体的地震、电磁特征，以及控矿构造和隐伏岩体平面分布的航磁异常特征.在地表地质和已知钻孔岩心及物性的约束下，构建了剖面的综合地球物理的地质解释模型，包括浅层推覆构造和控矿地层分布，推断解释大断裂6条，次级断裂16条和3处较大的隐伏岩体分布，为深入认识研究区的矿床成因和分布规律，指导在外围和深部找矿提供了地球物理有效响应特征.
Abstract:The Dapai polymetallic mining region,located in the south of the Datian-Longyan sub-depression belt in southwestern Fujian province,and on the west side of Zhenghe-Dapu deep fault zone,is considered as one of the largest polymetallic reserves in Fujian province. As exploration advances,finding the deeper and concealed deposits is urgently needed in this place and its adjacent areas. However,complex terrain and dense vegetation in Dapai deposit bring difficulties to geophysical investigations,especially for high-precision and large-scale surveys. Therefore,the understandings of the concealed ore-controlling structures,ore-bearing horizons and the distribution of igneous rocks are far from meeting the needs of deep prospecting. Under the guidance of metallogenic theory and prospecting model,the reflection seismic characteristics of the shallow thrust nappe ore-controlling structures and ore-bearing horizons have been extracted by using the reflection seismic method,2D inversion of controlled source audio frequency magnetotelluric method (CSAMT) data with terrain and 3D constrained inversion of aeromagnetic data. In addition,the seismic and electromagnetic characteristics of the Yanshanian igneous rocks that are closely associated with mineralization,and the aeromagnetic anomaly characteristics of the ore-controlling structures and the plane distribution of the concealed rock masses have also been obtained. Thereafter,a geological model,which contains shallow nappe structures and distribution of ore controlling strata,in a main section of this region have been established with the constraints from the geology and the physical properties of known drilling cores. Moreover,6 major faults,16 secondary faults and 3 large concealed rock masses have been deduced. All these results provide effective geophysical response characteristics for further understanding the genesis and distribution of ore deposits in the study area and guide prospecting in the periphery and deep spaces in this area.
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Key words:
- Southwestern Fujian /
- Dapai deposit /
- Geophysical response
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图 1
研究区构造地质图(修改自李培等，2019)
Figure 1.
Simplified structural geological map of the study area (modified from Li et al., 2019)
图 4
研究区地质图和测区测线位置图(地震和CSAMT剖面)
Figure 4.
Geological map with survey line location of Dapai deposit (seismic and CSAMT profiles)
图 5
(a) 航磁总场磁异常；(b) 航磁化极异常；(c) 区域磁异常；(d) 剩余磁异常
Figure 5.
(a) Aeromagnetic total field magnetic anomaly; (b) Reduced-to-pole magnetic anomaly; (c) Regional magnetic anomaly; (d) Residual magnetic anomaly
图 6
反射地震真地表深度偏移成像
Figure 6.
Depth migration imaging of reflection seismic data from real surface
图 7
(a) CSAMT数据采集观测系统；(b) CSAMT源与测试位置图
Figure 7.
(a) Data acquisition and observation system of CSAMT; (b) The source of CSAMT and its location
图 9
研究区推断断裂和磁异常线性特征叠合
Figure 9.
The overlap of fault inference with magnetic linear features of the study area
图 10
研究区断裂推断图(a)在区域磁异常上的叠加图；(b)在剩余磁异常上的叠加图
Figure 10.
The deduced faults in the study area overlay image on (a) regional magnetic map; (b) residual magnetic map
图 12
岩心的岩性及其合成地震记录
Figure 12.
The lithology and the synthetic seismic trace of (a) zk1001, (b) zk2001
图 13
连井地震剖面，右图为左图的放大显示
Figure 13.
Well seismic profiles, the right picture is the enlarged display of the left one
图 14
地震剖面、电阻率剖面、磁化率剖面综合解释断层和岩体
Figure 14.
Joint interpretation of faults and magma invasion from seismic profile, resistivity profile and magnetic susceptibility profile
表 1
岩心物性参数表
Table 1.
Physical properties of drilling core
序号 岩性 P波速度(m·s-1) 密度(g·cm-3) 波阻抗(105 cm2·s) 样本个数 1 灰岩 5864 2.6 10.72 5 2 泥岩 5923 2.57 7.50 5 3 大理石 3946 2.57 6.35 5 4 磁铁矿 6511 3.65 19.81 2 5 铅锌矿 6403 3.05 18.64 4 6 矽卡岩 4800 2.55 - 5 7 花岗岩 5490 2.65 11.06 5 
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