利用镜质体反射率方法寻找隐伏岩体--岩浆热场应用的一个实例

Vitrinite Reflectance Method to Identify Concealed Intrusion:An Example of Application of the Magmatic Thermal Field Theory

寻找隐伏岩体是热液矿床找矿中一项重要的任务。识别隐伏岩体的方法很多,如磁法、电法、重力法等,很多很有效。但是,缺少了一个既直接又简便的方法:镜质体反射率方法。岩浆侵位必然在周围形成一个热场,且随着距离岩浆的远近形成一个温度梯度场,叠加在地热场之上。因此,依据岩浆热场的变化即可发现隐伏岩体。如果我们能够知道隐伏岩浆的性质、围岩的热传导参数,甚至可以定量地查明隐伏岩体的深度、位置和规模。本文介绍煤田和石油地质部门最常用的镜质体反射率(vitrinite reflectance,以Ro表示)方法,具有简单、经济、有效、实用、快捷的优点。利用该方法识别隐伏岩体的有效距离根据岩体规模、成分、深度不同大约在几米至几公里范围。无论新老矿区,只要有志留纪以后的含泥质的岩石,都可以尝试采用这种方法。该方法既适用于地表也适用于钻孔。对于老矿区,有条件开展三维立体层面上的研究;新矿区钻孔少,应注意了解钻孔不同深度Ro变化的情况,尤其注意钻孔中某些深度Ro突变的情况以及随钻进深度增加Ro变化的情况,以便及时指导找矿。笔者认为,在矿区和非矿区,隐伏岩体的意义是不一样的。在矿区(无论新矿区老矿区),岩体与流体有相伴出现的可能性。如果在矿区发现Ro出现异常(Ro>2%),则应注意考察是否有与隐伏岩体相伴的矿化的可能性。笔者希望将该方法引入到矿床学研究中来,并结合热液金属矿床成矿作用的特征,开拓出新的应用前景,推进深部找矿取得新的进展。

It is of crucial important to identify the undiscovered intrusions in hydrothermal deposit prospecting. There are lots of effective methods to identify undiscovered intrusions, such as magnetic, electric, and gravitational methods. However, the vitrinite reflectance method for the geothermal indicator is a direct and simple method. Magmatic emplacement is bound to form a thermal field around, and form a temperature gradient field with the distance of magma and superimposed on the geothermal field. Therefore, we can find undiscovered intrusions through analysis of the variation of thermal field. If we know the heat transfer parameters of magma and surrounding rocks, we even can quantitatively determine the depth, the location and the scale of the undiscovered intrusion. The vitrinite reflectance（expressed as a Ro） method commonly used in coal and petroleum geology is a simple, economic, and effective method to identify undiscovered intrusion. The effective distance of the method is around a few meters to a few kilometers, depending on the size, composition, and depth of different intrusion. Regardless of the new and old mining area, you can try this method so long as there is post-Silurian mud rock. This method applies to the surface can also be applied to drilling. For old mining area, there are the research data for three dimension images, for new ones, the depth of Rovariation should be noted in order to guide the prospecting work in time. The authors argue that the intrusion is commonly associated with the fluid flow in the mining area. If Ro anomalies（Ro〉2%） are found in the mining area, attention should be paid to the possibility of undiscovered intrusion and the accompanying mineralization in geological expectations. The authors hope that the introduction of this method, combining with the characteristics of hydrothermal ore deposit to the study of ore mineralization, will carve out a new application and make new progress in the deep prospecting.