多尺度综合地球物理探测:揭示成矿系统、助力深部找矿——长江中下游深部探测(SinoProbe-03)进展

两个原因使我们必须开展深部探测.一是寻找深部资源,二是更好地理解形成和控制陆内成矿的深部动力学过程,预测新的矿集区.在深部探测专项、国家自然科学基金和地质调查项目资助下,作者在长江中下游成矿带及邻区开展了系统的多尺度、综合地球物理探测.包括:成矿带尺度的宽频地震探测及"廊带式"综合探测,矿集区尺度的骨干剖面探测和三维建模,矿田尺度的三维探测与反演模拟.探测结果在三个层次取得了一系列新认识和新发现,完善了相关探测方法技术.主要包括:揭示了成矿带岩石圈结构、深部过程及对成岩、成矿的控制,提出了成矿带形成的动力学模型,诠释了在狭窄的成矿带内形成大规模金属堆积的深部因素;揭示了典型矿集区地壳三维结构、组成和断裂分布,建立了矿集区三维结构模型和区域成矿模式,推断了主要控矿岩体、地层的空间展布,预测了新的找矿靶区;开展了"玢岩型"、斑岩型和热液型多金属矿床综合地球物理探测试验,总结了勘查模式,预测了深边部找矿靶区;提出了硬岩区反射地震数据采集设计、激发到接收的有效措施,探索了地震弱信号提取、噪声压制、静校正和偏移等处理新技术、新方法;提出了强电磁干扰区电磁去噪的数字形态滤波等技术,完善了二/三维带地形和考虑各向异性情况的电磁正反演技术.

Multi-scale and integrated geophysical data revealing mineral systems and exploring for mineral deposits at depth: A synthesis from SinoProbe-03

There are two reasons make it essential to explore the deep, one is the need for deep mineral exploration, and the other better understanding the deep dynamic processes that control the formation and distribution of major ore deposits, particularly, in the intra-continental setting. Financed by the SinoProbe (China's largest national collaborative, multidisciplinary Earth science research project), National Nature Sciences foundation and Chinese Geological Survey, the authors have conducted multi-scale and integrated deep exploration across middle and lower reaches of Yangtze Metallogenic Belt (YMB) and its major ore districts in Eastern China. These data range in scale from terrane and belt, district to camp-scale. The methods included broadband seismic, deep reflection seismic, wide-angle reflection/refraction, magnetotelluric sounding and gravity and magnetic modelling. The results provide first-order insights into physical and structural properties of the lithosphere and upper mantle beneath the YMB. These insights provide geodynamic clues and constraints as to why YMB is so well endowed in metals. The results also provide first-order constraints for the upper crustal structure, composition and fault distribution of major ore districts. Based on these information at depth, the three dimension geological model was constructed, which provides knowledge of the depth extent of subsurface or ore-controlling geologic units (e.g., faults, strata, and intrusions) that thus leads to a new targeting for deep mineral. Some typical exploration models for "porphyry" iron, porphyry copper and hydrothermal polymetal deposits were summarized through the 3D integrated geophysical methods test, and deep potential for exploration was evaluated around the deposits. In term of technical progresses, a series of measures were taken from acquisition parameter design, shooting to receiving. New methods from weak seismic signal extraction, noise suppression, static to pre-stack migration were proposed and tested. Mathematical morphology filtering and other denoising techniques, and 2D/3D forward and inversion methods considering the influence of the topography and anisotropy were proposed in the magnetotelluric sounding (MT) data processing.