Regional metallogenic pedigree refers to the orderly relationship between multiple metallogenic systems formed in different geological periods, the development and evolution of regional geological tectonic environment and the staged evolution of mineralization in specific metallogenic regions (Zhai Yusheng, 1999).
Regional metallogenic pedigree can also be broadly understood, such as "the metallogenic evolution history and distribution law of specific metallogenic regions are called metallogenic pedigree" and "it is feasible and necessary to take metallogenic series as the basic unit in order to reflect the characteristics of metallogenic evolution concisely" (Chen Yuchuan et al., 200 1).
(A) the correlation between metallogenic systems in different periods
In different geological periods of regional and global mineralization, there are many different forms of morning and evening correlation between different metallogenic systems:
1. Inheritance transformation relationship (inheritance)
Refers to the replacement of one metallogenic system by another in the process of geological history. That is, ore-forming materials exist forever, but what kind of metallogenic system they participate in changes with the transfer of time, place and conditions. Take iron ore as an example. Archean-Early Proterozoic was a banded ferrosilicon formation (BIF) metallogenic system (dominated by magnetite), and evolved into a marine ferromanganese metallogenic system (dominated by hematite) in Paleozoic. When the ancient BIF system is subjected to regional fracture-remelting, it can join iron-rich molten magma to form Mesozoic skarn iron ore system or volcanic-subvolcanic iron ore system. For another example, primary gold, tin, titanium, diamond and other metallogenic systems can be transformed into their own placer metallogenic systems after weathering and denudation on the surface.
2. Cracking relation (discreteness)
In the paleogeological period, due to the simple structure of mantle and crust and simple ore-controlling factors, some blocks (or mantle plume) rich in metal ore-forming elements were not decomposed and differentiated strongly and thoroughly, thus forming a metallogenic system that could maintain the original coexistence of multiple components. For example, the Cr, Ni, Cu, (Pt, V, Ti, Fe) metallogenic system in the mafic-ultramafic layered complex in Bushveld Craton, South Africa, is a rare giant metallogenic system in the world and has great economic value. However, this multi-component metallogenic system is rarely found in the later geological history, and it is speculated that it may be decomposed into three metallogenic systems: ① iron, vanadium and titanium metallogenic systems related to plagioclase-syenite; ② Ni, Cu and ∑Pt metallogenic systems related to calcium-rich mafic-ultramafic rocks; ③ Cr(∑Pt) metallogenic systems related to mafic-ultramafic rocks. From this inferred example, it can be seen that in the long-term evolution of geological history, the evolution direction of ore-forming materials in a certain rock layer from complex to simple is worthy of attention. The Mesoproterozoic Cu-U-Au-Fe-REE-F deposit in the Olympic Dam in Australia is also an example of the ancient multi-component ore-forming system, and whether there are pyrolysis products in the late geological history is also a question to be discussed.
3. Compound superposition relationship (compound superposition)
In some metallogenic areas (belts), there is a morning and evening composite superposition relationship between different metallogenic systems. The metallogenic system formed in the late stage is often superimposed on the metallogenic system formed in the early stage, that is, it repeats in time and space, resulting in complex reorganization, transformation and superposition. For example, Baoshan polymetallic ore field in northern Guangdong Province was a marine volcanic-sedimentary iron-copper metallogenic system of Middle Devonian in the early stage, and a hydrothermal tungsten-molybdenum metallogenic system related to Yanshanian silicon-aluminum intrusive rocks was developed in the late stage. In the sub-dacite porphyry distribution area in the middle of the ore field, the superposition and reorganization of these two metallogenic systems are very obvious. It is precisely because of the superposition of late Paleozoic volcanic-sedimentary metallogenic system and Yanshanian magmatic-hydrothermal metallogenic system that the polygenetic compound model of Dabaoshan ore field was formed. Stratigraphic skarn deposits such as Tongguanshan and Dongguashan in Tongling, Anhui Province are the result of composite superposition of iron-sulfur gypsum metallogenic system deposited in Carboniferous Huanglong Formation (C2h) and Yanshanian magmatic-hydrothermal copper-molybdenum-gold-iron-sulfur metallogenic system. Wushan copper-gold deposit in northwest Jiangxi is also a similar example of composite mineralization.
In addition to the above examples, the mineralization process of Bayan Obo rare earth niobite deposit is complex, which may be the result of composite mineralization of Mesoproterozoic rift sedimentation-magmatism and Caledonian magmatic hydrothermal process.
It should be emphasized that there are multicycle tectonic movements in China. Due to the inheritance of tectonic evolution, there are more opportunities for diagenetic and metallogenic systems in different geological periods to overlap in the same metallogenic belt. Regional mineralization often has the characteristics of multi-stage compound. This not only produces a considerable number of polygenic deposits, but also causes the complexity and diversity of composition and structure of some deposits, which is also an important condition for the formation of large-scale deposits.
(2) Examples of regional metallogenic pedigree.
1. example 1: metallogenic pedigree of regional deposits in the middle and lower reaches of the Yangtze River
The metallogenic belt in the middle and lower reaches of the Yangtze River has experienced three stages of structural development from late Archean to early Proterozoic: basement formation, caprock deposition and intraplate deformation. In the caprock stage, the Mesoproterozoic coastal sedimentary phosphorite series (Feidong, Susong and other places) were mainly formed. From Sinian to Cambrian platform sedimentary cover stage, siderite-pyrite (anhydrite) metallogenic series (such as Simenkou, Majiashan sulfur deposit and Huangmei siderite deposit) were mainly formed. This series has little industrial significance, but it provides an indispensable stratum (lithology) for the formation of the main metallogenic series of the metallogenic belt (Yanshan iron, copper, gold and sulfur metallogenic series). At the beginning of Mesozoic, the main body of the Yangtze plate (northeast margin) docked with the Dabie block, and then the intraplate deformation stage began. With the Yanshanian mantle uplift and block movement, intense and extensive magmatic emplacement and volcanic sedimentation occurred, forming the Yanshanian hydrothermal iron, copper, sulfur and gold metallogenic series related to syntectic granitoids. This metallogenic series is superimposed on the Late Paleozoic sedimentary metallogenic series in many sections, and there is basically a complicated relationship of inheritance, superposition and transformation between them. At the same time, it appears in the east of Ningzhen together with syntectic granite and its metallogenic series, alkaline granite (represented by Suzhou granite) and its associated iron, niobium and tantalum metallogenic series, which has little industrial significance, but the hydrothermal altered kaolin deposit in the syenite porphyry vein derived from it has important economic value and a long mining history. In the metallogenic belt in the middle and lower reaches of the Yangtze River, the Mesoproterozoic sedimentary phosphorite metallogenic series is distributed on the surface of metamorphic rock area in the northern margin of the metallogenic belt. It is not clear whether there is an inheritance and evolution relationship with Yanshanian granite metallogenic series and Ningwu porphyrite iron ore and phosphate deposit series, which should be paid attention to in future research work (see Chapter 5 for examples).
2. Example 2: Metallogenic pedigree of regional deposits in northern Guangxi (according to Chen Yuchuan et al., 1995).
The Yangtze paraplatform and South China fold system structural belt below northwest Guangxi are distributed on the Jiangnan axis in the northern part of this area, exposing Proterozoic strata. The Bos Group, the oldest basement stratum, is a set of metamorphic basic and ultrabasic rocks. The volcanic rock series consists of copper-nickel mineralization layer and layered tourmaline and cassiterite accumulation layer, with the oldest age of 24 1.2 billion years, belonging to Proterozoic. Jiangnan Axis is an arc-shaped structural belt in Guangxi protruding southward. It is a late Paleozoic marine clastic rock and carbonate rock deposit on the Caledonian fold basement, which experienced Indosinian orogeny. In Hechi-Nandan area, as the southwest edge of the earth axis, a fault depression was formed in Hercynian, thick flysch carbonate strata were deposited, Indosinian-Yanshan movement formed a close linear fold, and granite intrusion and mineralization were strong. From Proterozoic to late Yanshanian, five metallogenic series were formed with tectonic movement (Table 3- 19): copper, nickel and tin metallogenic series related to Bao Si mafic-ultramafic magmatism in Yuanbaoshan area; The metallogenic series of tin, copper and polymetallic deposits related to Xuefeng granite in Baotan area: the metallogenic series of tungsten-tin deposits related to Caledonian granite in northeast Guangxi; the metallogenic series of lead-zinc-sulfur deposits related to Hercynian-Indosinian intermediate acid magmatism on the edge of Jiangnan axis; Metallogenic series of nonferrous, rare, rare earth and uranium deposits related to Yanshanian granite in Nanling area.
(3) Study on regional metallogenic pedigree.
(1) The study of metallogenic pedigree is regional, and it is a macroscopic historical study of the internal relations between various deposits and their mineralization in a metallogenic area. This relationship involves a wide range, and the author suggests that the evolution of metallogenic system should be the basic research content of metallogenic genealogy, which can play an important role in outlining.
(2) According to the existing documents of metallogenic pedigree, the metallogenic pedigree is studied in a broad sense and a narrow sense. Broadly speaking, it refers to the whole evolution history of geological mineralization in a certain area, which is manifested by the differences in metallogenic tectonic environment and mineral deposit series. The narrow sense of metallogenic pedigree refers to the genetic relationship between successive metallogenic systems in the region, that is, there are genetic "genes" such as the inheritance, transformation and transformation of metallogenic materials and the genesis of ore deposits between successive metallogenic systems mentioned in this paper. This paper advocates the narrow concept of metallogenic pedigree.
Table 3- 19 Basic characteristics of ore-forming series in northern Guangxi
(3) To study the narrow sense of metallogenic pedigree, it is necessary to find out the internal relations (mainly genetic relations) among various metallogenic systems. Due to the transformation or even destruction of pre-existing deposits and metallogenic systems by geological processes in the late stage of geological evolution, the characteristics of many links in the metallogenic process have disappeared or nearly disappeared, and the information of metallogenic history is incomplete, which is difficult to study. In addition to studying the controlling effect of the change of geological tectonic environment on mineralization in the region, it is necessary to study various tracer marks such as trace elements, rare earth elements and isotopic compositions in ores and rocks in depth and systematically, and to explore whether there is genetic relationship between various deposit series. This is a comprehensive study with overall situation and a high-level subject of regional mineralization research.
(4) The study of regional metallogenic pedigree is a complicated work, which needs to be explored repeatedly and deepened not only for newly opened metallogenic belts, but also for those with high research level. A comprehensive understanding of regional metallogenic pedigree needs the continuous improvement of the whole earth system science.