成矿单元划分原则和方法探讨

A tentative discussion on the principle and method for division of metallogenic units

本文强调,区域成矿图的编制原则和方法虽然应当以大地构造为基础,但却更应考虑成矿作用本身。成矿作用本身是确定成矿单元及其边界的首要因素。笔者在文中仍采用了成矿省这一概念。但与前人的用法不同,在这里,成矿省不仅具有空间概念,更为重要的是它具有时间属性。本文所说的成矿省是指在一定大地构造基础上,在相同或相似的地质背景中,在相同或相近的成矿时代,经相同或相关的成矿作用所形成的一种或彼此相关的几种矿床的分布范围。在此基础上划分成矿区(带)、成矿潜力区和成矿远景区。成矿区(带)是指根据所存在的矿床分布情况和成矿有利地质条件划分出的成矿单元。成矿潜力区是根据成矿有利地质条件划分出的成矿单元;潜力区内有时会存在有关矿床的矿化显示。成矿远景区是根据成矿有利地质条件推测(预测)出的成矿单元。根据这一思路,笔者提出了成矿单元的划分步骤以及在大地构造基础上划分成矿单元的原则框架,将克拉通地区的成矿单元按克拉通基底发展阶段、克拉通盖层发展阶段和后克拉通发展阶段划分成矿省;将造山带地区的成矿单元按造山带发展早期阶段、造山带发展晚期阶段和后造山带发展阶段划分成矿省;与基性-超基性岩带有关的矿床按其发育的断裂带、裂谷带和蛇绿岩带划分成矿单元。在克拉通和造山带晚期特别是后期发育的成矿单元,其界线可能与大地构造界线不尽一致甚至可能穿越构造界线。笔者结合中国情况对成矿单元进行了初步划分,例如华北克拉通东端的胶—辽菱镁矿-滑石-石墨成矿省、华北克拉通北缘的燕—辽铁-金成矿省、西秦岭华力西造山带的西秦岭铅锌成矿省和大兴安岭华力西造山带的大兴安岭多金属-铁成矿省以及这些成矿省中的成矿潜力区和远景区等等。这样的划分,实际上已经预示了找矿范围和找矿方向。

It is emphasized in this paper that,so far as the principle and method for compilation of metallogenic map are concerned,mineralization itself should be more preferentially taken into consideration,though tectonic setting is the basis.Mineralization itself is the first important factor in delineation of a metallogenic unit and its boundary.The authors still use the term metallogenic province here.Nonetheless,different from previous usage,the term metallogenic province here has not only space attribute,but,what is more important,time attribute.The metallogenic province used here means an area where mineral deposits are distributed and formed due to the same or related mineralization in the same or nearly the same epoch and geological settings on a certain tectonic basis.Metallogenic regions（zones）,metallogenic potential and prospective regions are thus delineated.A metallogenic region（zone） is an area delineated on the basis of distribution of mineral deposits and favorable geological settings.A metallogenic potential region is delineated on the basis of favorable geological settings with or without known occurrences of mineralization therein.A prospective region is predicted or speculated in consideration of favorable geological settings for mineralization concerned.Following this consideration,the authors suggest a principal framework and steps to divide metallogenic units on the tectonic basis.Metallogenic units in cratonic areas are divided into metallogenic provinces of basement stage,cover stage and post-cratonic stage.Metallogenic units in orogenic areas are divided into metallogenic provinces of early stage,late stage and post-orogenic stage.Metallogenic units of mineralizations related to mafic and ultramafic rocks are delineated according to the fractures,rifts or ophiolite zones concerned.Boundaries of metallogenic units developed in late stages of craton or orogen,especially in post-cratonic or post-orogenic stages,may be discordant with or even traverse tectonic boundaries.The authors have primarily delineated some metallogenic units in consideration of the circumstance of China,for example,the Jiao（Shandong）-Liao（Liaoning） magnesite talc-graphite metallogenic province in the eastern end of the North China Craton,the Yan（Hebei）-Liao（Liaoning） iron-gold metallogenic province in the northern margin of the North China Craton,the West Qinling lead-zinc metallogenic province in the West Qinling Variscan Orogen and the Da Hinggan Ling polymetal-iron metallogenic province in the Da Hinggan Ling Variscan Orogen as well as metallogenic potential and prospective regions therein.This division,in fact,has implied and predicted prospecting areas.