Mineralization zoning

According to the statistics of 48 proven platinum group deposits, most of the platinum group deposits and occurrences in southwest China are concentrated in the center of Kangdian axis at the junction of Yunnan and Sichuan, but the largest Yangliuping and Jinbaoshan are located in the western margin of Yangtze platform.

Precambrian deposits and Phanerozoic PGE deposits are closely related to basic ultrabasic rocks. Even the Dayanzi hydrothermal deposit and the Sanjiawan jet sedimentary deposit are spatially related to basic ultrabasic rocks or dikes. Therefore, the distribution of basic-ultrabasic rocks reflects the spatial distribution of platinum group element deposits from a macro perspective. Generally speaking, basic-ultrabasic rocks in southwest China are widely distributed, although the exposed area is not large and it is difficult to be reflected on small-scale maps (Figure 7- 1). According to incomplete statistics, Fu Deming, summary of PGE mineral exploration in Sichuan .2001.10, p. 80.

There are 1 12 basic-ultrabasic rock groups in Sichuan province alone, including 1052 single rock bodies, with a total exposed area of about 640.68km2, including 643 ultrabasic rock bodies, 72 basic-ultrabasic rock complexes and 327 basic rock bodies. They are mainly controlled by regional deep belts in space and have linear distribution characteristics. From west to east, it can be divided into the following basic-ultrabasic rock belts: ① Jinshajiang rock belt; ② Dege-Xiangcheng rock belt; ③ Garze-Litang rock belt; ④ Luhuo-Daofu rock belt; ⑤ Kangdian rock belt; ⑥ Longmenshan rock belt; ⑦ Micangshan Rock Belt.

Magmatic rocks in different ore belts were formed in different times. Among them, Jinning basic-ultrabasic rocks are mainly distributed in Kangdian rock belt, Longmenshan rock belt and Micangshan rock belt, and layered basic-ultrabasic rocks are mainly found in Kangdian rock belt, with chromite and asbestos; Ring-shaped intermediate-basic complex was found in Longmenshan rock belt, and magnetite was produced. Alkaline ultrabasic rocks are found in Micangshan rock belt, accompanied by minerals such as titanomagnetite, nepheline bauxite and potash feldspar. Copper, nickel and platinum group minerals are mainly related to small and medium-sized ultrabasic rocks, which are found in Longmenshan rock belt (Tongsui) and Kangdian rock belt (Lengshuiqing). Hercynian basic ultrabasic rocks are mainly distributed in Kangdian rock belt and Jinshajiang rock belt. The former is mostly iron, producing large vanadium-titanium magnetite and copper, nickel and platinum group elements. The latter belongs to magnesium, ultramagnesium and chromite mineralization, accompanied by platinum group elements mineralization, which has the characteristics of high grade and extremely small scale. Indosinian basic-ultrabasic rocks are distributed in Jinshajiang rock belt, Dege-Xiangcheng rock belt and Ganzi-Litang rock belt, with a small scale and a large number. Some rocks in Jinshajiang rock belt and Dege-Xiangcheng rock belt have ultramafic characteristics and chromite mineralization, while ultrabasic rocks in Ganzi-Litang rock belt only have asbestos and magnetite mineralization. Generally speaking, the platinum group mineral resources in Sichuan are mainly concentrated in the Kangdian rock belt, and there are also many platinum group minerals in Yunnan, but the Kangdian axis belt is also the most widely distributed. Therefore, the Paleozoic layered basic-ultrabasic rocks in Panxi area, especially in Panxi area, are the main targets for prospecting platinum group elements at present.

Fig. 7- Distribution Map of Platinum Group Element Deposits in Southwest Margin of Yangtze Platform 1

1. Mineralization of basic-ultrabasic mafic complexes and platinum group elements in the granite terrane of Jinning continental margin.

This basic-ultrabasic mafic complex occurs at the junction of the margin of Yangtze Craton and Songpan-Ganzi orogenic belt and Qinling orogenic belt, and is distributed in Guangyuan-Beichuan-Baoxing, Kangding-Shimian-Xichang-Panzhihua areas. The main residual bodies are produced in granite terranes on the continental margin of the pre-Sinian period, or rock walls and rock-like intrusions are located in Mesoproterozoic strata; Controlled by pre-Sinian basement complex, it is distributed intermittently.

(1) Guangyuan-Wangcang rock belt

This rock belt is located in the east of Guangyuan in Nanjiang-Wangcang area, and the rock mass mainly intrudes into Proterozoic strata, which is distributed within a range of about 80km long (eastward into Hannan area of Shaanxi Province) and about 30km wide. There are mainly Yuquan, Cui Ying, Chunshuping and other rock bodies in Sichuan, and the scale is generally small (Yinwangshan rock body and Chengshan-Bijigou rock body in Hannan). The rocks include pyroxenite, lherzolite and amphibole peridotite, which have obvious crystal differentiation and rhythmic layer structure. Ultramafic rocks are mainly produced in the lower part of rock mass and are typical layered basic-ultrabasic mafic rocks. The diagenetic age is Mesoproterozoic (1 12 1Ma). Copper-nickel mineralization and magnetite mineralization can be seen in ultramafic rocks of layered basic-ultramafic rocks, and the evaluation of platinum content in ultramafic rocks has not yet been carried out.

(2) Guan Peng-Baoxing rock belt.

Basic-ultrabasic rocks are mainly distributed in Guan Peng complex in Maoxian-Dujiangyan area and Baoxing complex in Baoxing-Tianquan area. The main rocks are lherzolite, pyroxene gabbro and gabbro. Ultramafic rocks (most of which have been eroded into serpentine) mainly intrude into metamorphic basic-acid volcanic rocks-sedimentary rocks of Mesoproterozoic Huangshuihe Group, and occur along bedding, showing vein-like and layered emplacement. Guan Peng is mainly distributed in Hongyan, Mopan, Lanniwan and Huomayan. There are mainly Dengchigou and Lushan Baitongjianzi-Bulasijianzi ultrabasic dike groups in Baoxing area, which are mainly composed of peridotite, serpentine, pyroxenite and gabbro, with dozens of rock bodies. Copper-nickel sulfide mineralization was found in some ultrabasic rocks of Dengchigou and Lushan white copper base in Baoxing County, accompanied by platinum group element mineralization: Pt+Pd (0.0076 ~ 0.181) ×10-6. Cu-Ni-Pt sulfide mineralization body with Pt+Pd greater than the cut-off grade is found in Baitongjian ultramafic rock in Lushan County, which can be further studied.

Pyroxene-gabbro mainly occurs in Neoarchean-Proterozoic magmatic complex in the form of huge residues, mainly including Lengmugou, Xiaoyuxi, Huoshixi and Lushan Dachuan in Qionglai, which are generally large in scale, generally about tens of square kilometers, and the largest Lushan Dachuan rock mass can reach 150km2. Gabbro is dominant, with fine-medium-coarse grain structure and pegmatite grain size zoning characteristics, with good differentiation. There are rhythmic cycles composed of pyroxenite (peridotite) gabbro or fine-grained gabbro-coarse-grained gabbro and pegmatite pyroxenite-gabbro, which have the characteristics of banded, foliated structure and layered rock mass. Ultramafic pyroxenite, peridotite and gabbro usually appear at the bottom of rock mass. Cr and Ni anomalies often occur in the distribution area of this kind of rock mass, and there are copper-nickel mineralization, pyrite mineralization, magnetite mineralization and chromite mineralization in some areas. Pyritization, magnetite mineralization and sporadic chalcopyrite mineralization are found in the Dachuan rock mass in Lushan Mountain, with an average Pt content of 0.005× 10-6, a PD content of 0.005 1× 10-6, and a maximum Pt content of 0.023× 10-6.

(3) Kangding-Asbestos Belt

The distribution of rock masses in Jinning period is sporadic, and there are not many rock masses with a certain scale. There are Guzan and Kangding gas ditches in Kangding area, Lan 'an, Hong Jun Bridge, Shuijingwan, Vucko and Vucko in Luding area, and asbestos rock mass, Daheba and Caiyuanzi rock mass in asbestos area. Lithology mainly includes lherzolite, olivine pyroxene, pyroxene-gabbro, gabbro and so on. The M/F values of rocks are mostly between 2 and 6, belonging to iron ultramafic rocks, and chromite, titanomagnetite and a small amount of copper-nickel sulfide mineralization can be seen in some rocks. The rock mass mainly intruded into metamorphic basic acidic volcanic rocks-sedimentary rocks of Kangding Group from Neoarchean to Paleoproterozoic, and was eroded and cut by granite in the late Jinning period. Now it is generally a huge captive, and its origin is not easy to recover.

Asbestos Nanbei rock mass and Caiyuanzi rock mass group in asbestos area are mainly composed of dunite and plagioclase pyroxenite, and some pyroxenite and gabbro. Most of the M/F values of rocks are above 9, belonging to magnesium ultramafic rocks. Mineralization of asbestos, chromite, serpentine and talc can be seen in some rock masses. Natural platinum mineralization is found in pyroxenite of Daheba rock mass in Shimian area, and platinum group elements are mainly natural platinum. Other minerals include magnetite, ilmenite, pyrite and sporadic chalcopyrite. Platinum grade is between 0.2-3g/t, and the highest is about 30-40g/t, and the prospective reserves are above medium.

The working degree of basic-ultrabasic rocks in this area is generally low, but the same type of rocks are widely distributed and have certain prospecting potential.

(4) Miyi-Huili rock belt

Jinning basic-ultrabasic rocks are mainly exposed in Miyi, Panzhihua and Huili areas, including Gaojia Village in Yanbian (Lengshuiqing), Miyiyakou, Aqi, Xinglong in Dechang and Huilixia Village.

The surrounding rocks of the rock mass are mainly clastic rocks-carbonate rocks mixed with volcanic rocks of Mesoproterozoic Huili Group and Yanbian Group. Basic-ultrabasic rocks are generally emplaced along bedding or along structures, mostly in the form of rock basins, bedrock or irregular veins. The exposed area of rock basin and bedrock is generally within a few to dozens of square kilometers; Vein intrusions are small in scale, generally less than 1km2. The main rock types are peridotite, hornblende peridotite, monlherzolite, pyroxenite, gabbro, hornblende gabbro and diorite. Most rock masses have layered structure and banded structure, ultrabasic rocks generally occur along the bottom and core of rock masses, and the upper and edge of rock masses are generally basic rocks. Most of the rock masses are mineralized with chromite, vanadium-titanium magnetite and copper-nickel sulfide, and some rock masses in Gaojiacun (Lengshuiqing) and Miyiyakou in Yanbian have formed copper-nickel sulfide deposits with industrial value.

The evaluation of platinum-bearing rock mass in this area has not been fully carried out, but PGE is analyzed and tested by using previous geological data, and PGE anomalies and certain mineralization indicators are found. According to statistics, the high PGE content in Gaojiacun rock mass in Yanbian generally occurs in ultrabasic rock mass at the lower part of each rhythmic layer of the complex, with an average content of 20× 10-9 ~ 55× 10-9, with the highest values reaching 26 1× 10-9 respectively. However, the content of basic rock units in the upper part of each rhythmic layer basically remains between1.7×10-9 ~ 3×10-9; It shows the enrichment characteristics of PGE in ultrabasic rocks. Although no valuable platinum-rich horizon has been found, the current work shows that the rock mass has further work value.

2. Mineralization of basic-ultrabasic rocks and platinum group elements related to Emei mantle plume in Hercynian.

The complex belt occurs in the Danba-Xiaojin-Longmenshan Trigeminal Rift, Panxi Rift and Jinsha River, Ganzi-Litang and Xianshuihe structural belts at the junction of Yangtze Craton and Songpan-Ganzi orogenic belt and Qinling orogenic belt. Basalt has a huge distribution range, and basic-ultrabasic rocks mainly invade Paleozoic strata and are distributed along basalt distribution areas and structural zones.

(1) Guan Peng-Baoxing and Tianquan rock belt

Hercynian basalts are widely distributed in this area, and basic-ultrabasic rocks that are out of phase with basalt eruption at the same time are relatively few and scattered in this area, mainly peridotite (serpentine) pyroxenite, gabbro and gabbro, which generally intrude in veins and layers in Paleozoic strata. The basic-ultrabasic rock mass with relatively large scale is Tian Quan Yanping complex, and Cu-Ni-Pt sulfide mineralized bodies have been found in vein intrusions around it.

Tianquanyan oblate complex is exposed at the dip end of Qianchanggou complex anticline, and intrudes into Paleozoic shallow metamorphic rock series, forming basic-ultrabasic rock groups with nearly annular distribution. Nearly 30 basic-ultrabasic rocks have been found in this area, most of which are irregular layered, lenticular and veined, with different scales. Rock types include lherzolite, pyroxene peridotite, olivine pyroxene, pyroxene-gabbro and gabbro-diabase. Ultrabasic rocks (lherzolite, pyroxene peridotite and olivine pyroxene) have intrusive contact with basic rocks (gabbro). At present, Cu-Ni-Pt mineralized ore bodies have been found in basic-ultrabasic dikes, which have certain prospecting potential.

(2) Danba-Kangding Rock Belt

Hercynian basic-ultrabasic rocks are widely distributed in this area. There are dozens of large and small rock masses near 120km along the Danba-Kang Ding Sandao Bridge, and the surrounding rocks are mainly a set of terrigenous clastic rocks-carbonate rocks (including basic volcanic sedimentary rocks) of Silurian and Devonian. Basic-ultrabasic rocks in this area are associated with Permian marine basalt, which constitutes a part of the famous Permian igneous province at home and abroad.

The basic-ultrabasic rocks in Danba area are mainly distributed in Yangliuping, Stone Shed and Yuhaizi in Danba. Rock mass is exposed in the core and wing of the nearly elliptical dome anticline (dome structure) in this area, and occurs in the form of rock basin, bedrock or irregular layer-like, forming a nearly annular distribution of rock mass groups. The main rock types are serpentine, amphibole, sub-amphibole, gabbro and a small amount of diabase, and the original rock recovery belongs to amphibole-pyroxenite-gabbro series. Evolution products of different stages at the same time as the overlying basaltic magma. At present, Cu-Ni-Pt sulfide ore bodies of different sizes have been found in Yangliuping, Shitoupeng and Yuhaizi ultrabasic rocks, among which Yangliuping Pt-Ni deposit is the largest. In recent years, through the evaluation of platinum minerals in basic-ultrabasic rocks in Shibaote and Yuhaizi areas in this area, it is found that platinum group elements are well displayed, which proves that there is still great prospecting potential in this area.

Basic-ultrabasic rocks in Kangding area are mainly distributed in Erdaoqiao, Xinxing and Wudaoniupeng areas in northern kangding city, and bedding intrusions of rock mass are located in a set of terrigenous clastic-carbonate sedimentary rock series of Silurian and Devonian in this area. The main rock types are peridotite, pyroxenite, gabbro and a small amount of diabase, covered with Permian marine basalt. The tectonic geological background and magmatic evolution series of basic-ultrabasic rocks are basically the same as those in Danba area, but the rock mass is relatively small and scattered. Mineralization of asbestos and magnetite has been shown, but platinum group minerals have not been evaluated.

(3) Luding-Asbestos Rock Belt

Basic-ultrabasic rocks in this belt are mainly distributed in Paleozoic strata in the west of Archean-Proterozoic basement complex (Kangding complex), with scattered rock masses and small scale. There are mainly lherzolite, olivine pyroxenite, pyroxenite, gabbro, gabbro and so on. The M/F value of rocks is mostly between 2 and 6, which belongs to iron ultramafic rocks. They are generally vein-like and layered intrusions in SILURIAN and Devonian terrigenous clastic rocks-carbonate sedimentary rocks, and are the products of homologous magma evolution with Permian marine basalt series. Some large rock masses can be divided into zones in composition and structure, and chromite, titanomagnetite and a small amount of copper-nickel sulfide can be seen locally. Ultrabasic rocks in asbestos area are produced by magnetite with different scales, and are being mined on a small scale at present, and the platinum content in rock mass has not been evaluated yet.

(4) Mianning-Huili rock belt

This area is an important basic-ultrabasic rock belt in Sichuan, with a length of about 180km and a width of about 50 ~ 100 km. There are more than 100 basic-ultrabasic rocks, which are mainly exposed in Mianning, Panzhihua, Miyi and Huili areas. Panzhihua Mianning Guihua Village, Baima, Hongge, Taihe, Miyi New Street, Huilima River, Dayazi and other representative rock masses. The surrounding rocks are mainly clastic-carbonate sedimentary formations of Devonian, Carboniferous and Lower Permian, with a small amount of pre-Sinian basement complex (Kangding complex). The rock mass is closely related to Permian Emeishan basalt, and its diagenetic age is similar. Generally occurring in rock strata, rock basins, bedrock or irregular veins. Rock mass is generally large, and the exposed area is generally within a few to dozens of square kilometers. There are clinopyroxene pyroxene-gabbro, gabbro, gabbro-diabase series and dunite-peridotite gabbro and gabbro series. The former is relatively rich in iron and has a typical layered structure, forming large-scale super-large vanadium-titanium magnetite, such as Panzhihua, Baima, Hongge and Taihe. The latter two have slightly higher Mg content, and the rock mass is smaller than the former, accompanied by copper-nickel and platinum-bearing copper-nickel mineralization.

Hercynian basic-ultrabasic rocks in this area are widely distributed and large-scale, mostly distributed in rock groups and belts. Increase investment in platinum mine exploration and make important progress; A number of important prospecting clues have been discovered successively, such as the large-scale vanadium-titanium magnetite PGE deposit in Miyi Street, the magmatic hydrothermal PGE deposit in Dayanzi, Huili, Qingshuihe and Daikuangshan, which prove that this area has great prospecting potential and is another important PGE enrichment area in Sichuan Province except Danba, and its resource reserves may exceed that in Danba area.