区域成矿学与矿产资源调查评价

蚀变类型（Alteration Types）
•青磐岩化Propylitic: (Chlorite, Epidote, Actinolite) 绿泥石、绿帘石、阳起石 Propylitic alteration turns rocks green, because the new minerals formed are green. These minerals include chlorite, actinolite and epidote. They usually form from the decomposition of Fe-Mg-bearing minerals, such as biotite, amphibole or pyroxene, although they can also replace feldspar. Propylitic alteration occurs at relatively low temperatures. Propylitic alteration will generally form in a distal setting relative to other alteration types.
一、蚀变、热液蚀变、蚀变带、蚀变矿化带
二、异常、矿化点、矿点、矿体、矿床、矿区、矿田、矿 化集中区（矿集区、矿化密集区）、成矿区、成矿带、成 矿系列、成矿省（成矿域） 三、远景区、靶区 三、小型、中型、大型、超大型矿床 四、成矿作用 以下重点介绍热液蚀变和蚀变带方面的知识：
蚀变（Alteration）
区域成矿学与矿产资源调查评价
——从概念到野外工作方法
第一部分Leabharlann Baidu
第二部分
从蚀变到区域成矿方面的概念与描述
有关成矿地质特征方面的概念与野外描述
第三部分
第四部分 第五部分 介
有关矿床类型方面的概念与描述
矿床发现的途径 蒙古人民共和国Oyu Tolgoi 斑岩型铜矿简
第一部分
从蚀变到区域成矿方面的概念与描述
•矽卡岩化 Skarnization
Skarnizations are replacement alteration. They form by the replacement of limestone, calcareous rocks (marl or calc-schist), or dolomite. A wide variety of minerals can form in skarn, but the most common include oxide minerals such as magnetite, sulfide minerals such as chalcopyrite, silicate minerals such as epidote, or the tungstate mineral Scheelite.
Example of proximal and distal zoning of base metal vein deposit of the type associated with porphyry copper/molybdenum deposits.
蚀变填图（Alteration Mapping）
•绢云母化 Sericitic:
(Sericite)
Sericitic alteration alters the rock to the mineral sericite, which is a very fine-grained white mica. It typically forms by the decomposition of feldspars, so it replaces feldspar. In the field, its presence in a rock can be detected by the softness of the rock, as it is easily scratchable. It also has a rather greasy feel (when present in abundance), and its color is white, yellowish, golden brown or greenish. Sericitic alteration implies low pH (acidic) conditions. Alteration consisting of sericite + quartz is called “phyllic” （绢英岩化）alteration. Phyllic alteration associated with porphyry copper deposits may contain appreciable quantities of fine-grained, disseminated pyrite which is directly associated with the alteration event.
蚀变带（Alteration Zoning）
Although mineral zoning patterns are not uncommonly developed around ore deposits, they are not always present or obvious. The patterns can be caused by changes in temperature, fluid chemistry or gas content. The change in parameters over time, such as decreasing temperature of the fluids, can cause overprinting of lower temperature minerals by higher temperature minerals. Structural deformation, such as when a rock shattering or faulting event affects the host rocks, can cause more complexity. Alteration zoning can occur in many different geometric forms, ranging from concentric shells, to linear forms, to irregular and complex. Porphyry copper deposits are characterized by concentric shell-shaped zones of alteration, which overlap to some extent Figure 8 – 1 A. The core area contains “potassic” alteration in the form of potassium feldspar and biotite. Further outward is a zone of “phyllic” alteration consisting of the assemblage quartz-sericite-pyrite. The outermost zone, called “propylitic”, is characterized by the assemblage quartz-chlorite-carbonate and locally containing epidote, albite or adularia. Epithermal deposits associated with major structures (faults or fractures) have linear zones which parallel the structure. The mineralogy is highly variable, as is the geometry. One example of alteration zoning associated with a volcanic vent is shown in Figure 8 – 1 B. This example indicates an inner zone of silicification forms within a central breccia formation, and an outer zone of propylitic alteration lies adjacent. Sericite is a common alteration mineral formed in zones along fault structures or fault zones in low to moderate temperature settings.
热液蚀变（Hydrothermal Alteration）
Hydrothermal alteration is a change in the mineralogy as a result of interaction of the rock with hot water fluids, called “hydrothermal fluids”. The fluids carry metals in solution, either from a nearby igneous source, or from leaching out of some nearby rocks. Hydrothermal alteration is a common phenomena in a wide variety of geologic environments, including fault zones and explosive volcanic features.
Rock alteration simply means changing the mineralogy of the rock. The old minerals grow are replaced by new ones because there has been a change in the conditions. These changes could be changes in temperature, pressure, or chemical conditions or any combination of hese.
Alteration can be mapped graphically using patterns or colors in much the same way that lithologic units are mapped. The primary characteristics to note are the alteration mineralogy, style and intensity. The mineral assemblages can be coded using patterns or colors. The style of alteration refers to the form, which could be disseminated or massive or anything in between. Another form of alteration is “veinlet-controlled”, which indicates that alteration is restricted to narrow zones adjacent to veinlets. The intensity of alteration refers to how well-developed the alteration is. It could be incipient mineral growth due to weak development, or it may be pervasive throughout the rock, indicating strong development. Mapping alteration can be used to predict mineralization. In theory, this is done by comparing the results of alteration mapping with known alteration zoning patterns for known mineral deposits. In practice however, the process is seldom so simple because every mineral deposit has some uniqueness to its alteration zoning.