The oldest stratum in this area is Baoban Group, which is a set of intermediate metamorphic rock series composed of staurolite mica quartz schist, amphibole schist, siliceous biotite schist and red pillar biotite schist, with a thickness of over 3000m. Its protolith formation is rifted trough continental margin sand argillaceous sedimentary formation. Zircon U-Pb age 1463.475Ma measured by mica schist can be regarded as the age of the formation of the cladding group (Yichang Institute of Geology and Mineral Resources, etc., 199 1). Shilu Group is not integrated on Baoban Group, and the unconformity between them may represent the early movement of Jinning about11000 Ma. Shilu Group is the ore-bearing stratum in Bentie metallogenic area, and it is a set of shallow metamorphic rock series composed of quartz schist, quartzite and carbonaceous slate. The lithology is divided into six layers from bottom to top, and the sixth layer is the ore-bearing layer. Total thickness 1700 ~ 2600 m, the original rock formation is a set of sandy argillaceous-carbonate sedimentary formations located at the continental margin of the Olla trough, with the characteristics of shallow sea-bay-lagoon facies, flysch rhythmic structure and acid volcanic eruption. From Shilu Group upward, the Sinian limestone top stratum is unconformity, which represents the late Jinning Movement. According to the Sm-Nd isochron age of metamorphic acid volcanic rocks in Shilu Group (Yichang Institute of Geology and Mineral Resources, 1990), it is inferred that Shilu Group belongs to Neoproterozoic Qingbaikou period.
In a word, Jinning movement is a strong tectonic movement in Hainan Island, especially in this area, which is mainly manifested by the strong folding of Baoban Group and Shilu Group, resulting in the unconformity contact between Baoban Group and Shilu Group, Shilu Group and Lime Top Group, accompanied by volcanic eruption and regional metamorphism. The nearly east-west syncline composed of Shilu Group and anticlinorium constitutes Shilu fold belt; Like the nearly east-west syncline composed of Baoban Group, Baoban syncline is the remnant of Jinning fold belt involved in Phanerozoic Yangtze-Qionghai structural belt.
Shilu iron deposit, located in Changjiang County, Hainan Province, is a famous large-scale iron-rich deposit in China and a major iron-rich production base in China. Shilu iron deposit has accumulated proven primary ore reserves of 398 million tons, and the amount of placer (mining)17.64 million tons, totaling 4160,000 tons, which is a super-large iron deposit. The average grade of the whole mining area is TFe5 1. 15%, including S0.493%, P0.0 19% and SiO2 19.44%, which is rich in blast furnaces (iron ore for ironmaking), in addition to copper, cobalt, dolomite and quartzite.
The mining area is located in Shilu Group, the composite part of Nanluo-Shilu syncline and Great Wall-Baisha east-west fault zone in the Yangtze River-Qionghai structural belt (Figure 5-4 1).
Figure 5-4 1 Geological Map of Shilu Iron Mine Area
(According to Yao Peihui et al. 1993)
P- Permian; Qn-Shilu Group; γ π-granite porphyry; 1- iron ore body; 2- copper ore body; 3- cobalt ore body; 4- granodiorite; 5- exploration line; 6- Drilling
Shilu Group is divided into seven layers from bottom to top: ① sericite quartz schist; ② Crystalline dolomite and diorite dolomite; ③ Timely sericite schist; ④ Quartzite and quartz schist; ⑤ sericite quartz schist; ⑥ It is mainly composed of crystalline dolomite, dolomitic crystalline limestone, diorite-diorite dolomite and diorite-diorite dolomite, with high siliceous and argillaceous content in some areas, sometimes with lamellae, phyllite and metamorphic sandstone lenses, and the lower part is mainly dolomite with a thickness of more than 500 meters; ⑦ timely sericite schist and quartzite, with thin hematite and ferromanganese deposits. The deposit occurs in the sixth layer of the upper part of Shilu Group. The main iron ore bodies and rich iron ore bodies occur in the middle and lower banded diopside diopside rocks, and the upper poor iron ore bodies occur in metamorphic siltstone. Cobalt and copper ore bodies occur in diorite-diorite dolomite in the lower part. The ore bodies are all layered and quasi-layered, which changes with the change of syncline fold shape. The iron ore body is the core, and the cobalt and copper ore bodies are distributed annularly outside the syncline. The ore bodies at the core of syncline tend to thicken and enrich (Figure 5-42), indicating that the ore bodies are controlled by horizons first, and then deformed by folds, and the bending flow of folds makes the ore bodies thicken and enrich.
Figure 5-42 Section of Line 8a of Shilu Iron Mine
(According to Yao Peihui et al. 1993)
Qn6—-6th floor of Shilu Group; Qn5—-5th floor of Shilu Group; 1- iron ore body; 2- copper ore body; 3- drilling; 4- cobalt ore body
Iron ore has flaky and massive structure, with scaly structure as the main structure, followed by residual silt structure. The main ore mineral is hematite, with minor magnetite and siderite locally. Cobalt and copper ores are mainly irregular network veins, which are banded and massive. The main ore minerals are cobalt-bearing pyrite, cobalt-bearing pyrrhotite and cobalt-nickel-copper mine, and the gangue minerals are mainly quartz, diopside, tremolite, barite and calcite.
The ore-controlling factors of Shilu iron deposit are mainly stratigraphic lithology control and structural control. Although a lot of scientific research and exploration have been carried out in the metallogenic area, the second Shilu iron deposit has not been found so far, so it is difficult to further explore.