For example, rift basin, aulacogen environment and regional synsedimentary faults are favorable tectonic environments for mineralization and favorable indicators for controlling the spatial distribution of metallogenic belts.
Second, the sedimentary phase change zone and the environmental mark of reducing geochemical barrier
The sedimentary phase transition zone and the relatively closed reductive geochemical barrier environment are favorable sedimentary environments for mineralization, while the Taigou facies zone and reef (beach) facies zone are favorable sedimentary environment signs for the formation of large and super-large deposits. Other sedimentary environment indicators favorable for hydrothermal deposition and mineralization are trough facies belt, limited-semi-limited platform facies belt, open platform facies belt and nearshore facies belt.
Three. Environmental signs of geothermal fields
The high paleogeothermal field is an environmental indicator of geothermal field favorable for mineralization, which is characterized by: volcanic rocks, subvolcanic rocks or dikes are produced in rift basins; Coal seams in sedimentary basins become anthracite with high metamorphic degree, such as Youjiang basin; There are modern hot springs in sedimentary basins; Sedimentary rock that produce hot water; Paleogeothermal values calculated from vitrinite reflectance, conodont discoloration index and asphalt reflectance.
Four. Marginal signs of ancient uplift
The edge of local ancient uplift in sedimentary basin is a favorable structural condition for mineralization, and this ancient uplift is often equidistant from its secondary sag. Therefore, the edge of local ancient uplift and its equidistant characteristics are important evaluation basis for finding target areas.
Five, synsedimentary fault logo.
Synsedimentary fault is a favorable structural indicator of hydrothermal sedimentary deposits. In addition to the above-mentioned regional synsedimentary faults, the intersection of regional synsedimentary faults and secondary synsedimentary faults is a sign of controlling ore fields and deposits. Within the scope of ore field or deposit, the intersection of sub-plane synsedimentary fault or fault bend is often the development site of hot water jet, so it is also a favorable location for mineralization and enrichment. Therefore, the faults in these parts are structural signs that control the output of ore deposits and ore bodies. The local depression near synsedimentary fault is a sign of layered mineralization and enrichment, while the synsedimentary fault at the bottom of the secondary depression or lateral uplift zone and the contact zone inside and outside the small rock mass is a sign of vein, reticular vein and breccia mineralization and enrichment related to hydrothermal deposition. Secondary synsedimentary fault and even local depressions often have the characteristics of equidistant distribution, which is also an important symbol of prospecting evaluation.
Six, stratigraphic and lithologic signs
Because of the different development and evolution characteristics of rift sedimentary basins, the ore-bearing strata have obvious regional characteristics in controlling mineralization. Qingxi Formation of Lower Cambrian is the main ore-bearing horizon of barite, vanadium and tungsten in northern Guangxi. The Middle-Upper Cambrian is the host bed of copper-tin deposits in southwest Guangxi. The Middle and Upper Ordovician-Lower Silurian is an important ore-bearing horizon of Pb-Zn-W-Cu polymetallic deposits in the early Paleozoic rift basin in southeastern Guangxi. Devonian is another global rift period, and it is also a global hydrothermal sedimentary metallogenic period, which is also very obvious in Guangxi. Devonian is the most important ore-bearing stratum in Guangxi. Devonian is the main ore-bearing stratum in Danchi, central and northern Guangxi in southwest Guangxi, and it is also an important ore-bearing stratum in southeast Guangxi, such as Guiping tin mine pit and Qingfeng lead-zinc mine, which are produced in Middle Devonian and Guiping Gui Mu manganese mine. Carboniferous and Permian are not important ore-bearing strata, but there are manganese and gold mineralization; Triassic is an important ore-bearing stratum, and Baifeng Formation, Banna Formation or Xinyuan Formation of Middle Triassic and Luolou Group-Ziyun Formation of Lower Triassic are the most favorable ore-bearing strata for hydrothermal sedimentary gold deposits in Guangxi.
Although different types of mineralization have different ore-hosting lithology, fine clastic rocks containing carbon and pyrite or carbonate-fine clastic rocks are favorable for ore-hosting, and pyrite often has strawberry structure. This lithology indicates a semi-closed and closed stagnant environment with low energy and hypoxia.
Seven, hot water sedimentary rock marks
The existence of hydrothermal sedimentary rocks is not only a sign of the genesis of hydrothermal deposits, but also an important petrological sign of prospecting evaluation. Generally speaking, barite rocks are mainly produced in the upper wall of ore bodies, and in the horizontal direction, they are produced on the edge of ore bodies slightly away from hot water vents; Siliceous rocks occur in most hydrothermal sedimentary deposits, generally closely associated with ore bodies, but in some deposits, siliceous rocks often occur in the footwall of ore bodies, such as gold mines, barite mines, barite-polymetallic sulfide mines and so on. Even though siliceous rocks are closely related to other mineralization, the siliceous rocks in the footwall of the ore body are more developed. Generally, the electrodeposited rocks in Guangxi are closely associated with tin ore or tin polymetallic ore, but from the occurrence characteristics of hydrothermal sedimentary electrodeposited rocks at home and abroad, there are also mineralization types such as copper, lead, zinc, gold, tungsten, iron and pyrite, and common electrodeposited rocks occur in the footwall of ore bodies. Layered skarns are generally closely related to ore bodies, that is, ore bodies occur in skarns. However, it should be noted that due to the high formation temperature of skarn minerals, the occurrence position of layered skarns is generally closer to hot water vents or vertically deviated from the footwall of ore bodies, so attention should be paid to prospecting and evaluation. Especially when there are both layered skarn and other hydrothermal sedimentary rocks such as siliceous rocks, barite rocks, iron ore or manganese carbonate rocks in the mining area, we should pay attention to the prospecting evaluation of polymetallic deposits between skarn and barite rocks or iron (manganese) rocks.
Eight, mineral deposit marks
The ore bodies in the mining area are mainly layered, layered or lenticular, which are integrated with the host rocks and have the characteristics of multi-layer output. Vein, net or lenticular ore bodies with the same ore composition can be produced in the footwall of layered ore bodies or nearby uplift areas. Ores have layered, banded, bean-like (oolitic), breccia-like and colloidal structures, as well as fine-grained, fine-grained and strawberry-like structures; Hydrothermal alteration is characterized by "bottom erosion structure" These are mineralogical indicators for evaluating the genesis of hydrothermal deposits.
IX. Traces of hydrothermal alteration
1) alteration types: in hydrothermal sedimentary deposits, most alteration types are strong, and the alteration types of different mineralization types are different, such as silicification, pyritization, electrochemistry, sericitization, skarnization, barite, dolomite, antimony mineralization, arsenic mineralization, chlorite-epidote mineralization, albitization, etc.
2) The alteration has the characteristics of "bottom erosion structure": except barite, most of the alteration is characterized by "strong bottom and weak top", that is, the footwall of the ore body is strongly altered, even reticulate vein altered rock tubes appear, and the upper wall of the ore body is weakly altered or even non-altered. This feature is one of the signs that the ore body is caused by hot water deposition.
3) Alteration zoning: The alteration in some mining areas can also be characterized by zoning, that is, from the spout outward, the alteration types evolved from anhydrous skarn-hydrous skarn, pyrrhotite → pyritization, silicification, sericitization, chloritization → barite → epidote and hematite (mirror) mineralization. Using this alteration zoning feature is beneficial to prospecting and evaluation.
Mineralization combination mark
Based on the common mineralization zoning characteristics of hydrothermal sedimentary deposits, the characteristics of mineralization combination are put forward. For example, Finlow-Bates put forward an ideal model of hydrothermal sedimentary deposits, and the mineralization zoning from the spout is: pyrrhotite, chalcopyrite → galena, sphalerite, pyrite → barite → hematite (Figure 7-1); Tu Guangchi et al. (1987) pointed out that barite deposits often have genetic and spatial relations with other deposits of a certain type. Based on the hot water nozzle, the general zoning trend is: polymetallic sulfide → barite → metal oxide (phosphorus, vanadium, molybdenum and uranium) → iron and manganese oxide. In the mineralization assemblage, copper, lead and zinc can coexist with pyrite and barite, and barite can coexist with phosphorus, vanadium, molybdenum, uranium and silver. For example, at the top of Jilongding in Rongxian County, copper, lead, zinc and silver coexist with pyrite; Lead, zinc and pyrite coexist in Pengcun-Panlong ore field; In Beishan, lead and zinc coexist with pyrite; In Huanong mining area, barite and pyrite coexist; Phosphorus, vanadium and molybdenum mineralization are associated in Sanjiang Banbi barite mining area; In Gutan barite mining area, uranium, molybdenum and manganese mineralization are associated; In Dafeng vanadium mine, silver mineralization is related. Wu Yi et al.,1987; Tu Guangchi et al.,1987; Zhao et al., 2000). Based on this spatial correlation, related mineralization types can be used as evaluation indexes for prospecting.
For another example, antimony, arsenic and mercury deposits, occurrences and mineralization points are important prospecting evaluation indicators of gold deposits in northwest Guangxi. Predecessors used "not in it, leaving no trace" to illustrate the relationship between gold deposits and antimony, arsenic and mercury mineralization (Liu Dongsheng et al., 1994).
XI。 Mineralogical marker
Mineralogical signs of different mineralization types are different, but one thing is that the occurrence of strawberry or colloidal pyrite is almost * * *, which is often * * with carbonaceous pyrite. Their occurrence positions indicate the position of secondary closed depressions in sedimentary basins, so they are also the signs of the occurrence positions of ore bodies.
For hydrothermal sedimentary gold deposits, the mineral combination of pyrite and arsenopyrite is an important mineralogical indicator. Strawberry pyrite is often an ore body, and irregular crystalline pyrite, irregular fine-grained aggregate, banded pyrite, arsenic-rich pyrite and needle-like arsenopyrite are all gold mineralization enrichment sites.
In hydrothermal manganese deposits, the development of rhodochrosite and its symbiotic position with black hard chlorite, manganese epidote, ferromanganese sphalerite, actinolite, rhodochrosite, brown manganese ore, hausmannite, hematite, magnetite and other minerals are mineralogical signs of the inner zone of hydrothermal activity and the zone near hot water vents. When manganese silicate minerals such as rhodochrosite are missing from the ore, they are mainly mineral combinations such as manganese calcite, calcium rhodochrosite, Yingshi, illite and chlorite. It shows that mineralization is far from the jet center and located at the edge or upper part of the ore body.
Twelve. Geochemical marker
Due to the differences in geochemical characteristics of elements, there is a widespread phenomenon of polymetallic element zoning centered on hot water vents in hydrothermal sedimentary deposits, which is of great guiding significance for prospecting evaluation.
1. Geochemical Significance of Iron with Different Valences
In the ideal zoning model of hydrothermal sedimentary deposits, iron can be distributed in each zoning, generally in the form of pyrite. However, if it occurs in the form of reduced iron, that is, pyrrhotite (Fe 1-xS), it indicates that the relatively reduced environment exists at the bottom of vein ore or layered ore near hydrothermal vents. If it is iron oxide, that is, hematite and specularite (Fe2O3), it indicates that it is in a relatively oxidized environment, indicating that its occurrence position is at the edge and upper part of the ore body far from the hot water spout (Figure 7- 1).
Fig. 7- 1 Ideal metallogenic model of hydrothermal sedimentary deposits (according to Finlow-Bates, 1987)
2. Geochemical characteristics of iron and manganese
Because of the different geochemical characteristics of iron and manganese, the zoning of iron and manganese is obvious in the process of hydrothermal deposition and mineralization. Iron precipitates earlier than manganese, and manganese is more widely distributed and farther from the center of hot water jet because it precipitates later than iron. For example, the iron-manganese zoning phenomenon of Zhailim-Karazare iron deposit is very obvious (Figure 7-2). Hanfa et al. (1997) pointed out that in Changpo-Tongkeng deposit, the iron content in ore body is high and the manganese content is low. The surrounding rock at the top of the ore body contains high manganese and low iron, but in the upper part of the ore-bearing formation, a siliceous manganese-bearing layer appears in the Duolihuosi limestone of Upper Devonian Wuzhishan Formation, which fully reflects the obvious zoning characteristics of iron and manganese separation. Therefore, it can be considered that the anomaly of manganese geochemical halo formed during hydrothermal deposition and mineralization is a remote indicator of the location of ore-accumulation stagnation basin or deposit.
3.Co/Ni ratio
Peng Zhangxiang (199 1) pointed out that the Co/Ni ratio is a geochemical indicator indicating the distance between manganese ore and volcanic eruption source, and its indicators are as follows: the short-range Co/Ni value is less than 0.55, which is an important indicator for finding rich manganese ore (Heqing manganese mine); The medium-range Co/Ni value is 0.55 ~ 1 (Xia Lei manganese mine); The remote Co/Ni value is greater than 1 (Jiaodingshan manganese mine).
As mentioned above, the Co/Ni ratio is less than 1, so it can be considered that the Co/Ni ratio can be used as an index to judge the distance between the hot water deposit and the jet center.
4. Evaluation criteria for geochemical prospecting of gold deposits
According to the research of Guangxi Geophysical Exploration Team (199 1), the axial zoning of primary halo of gold deposits in northwest Guangxi is As-Sb-Li-Au-Hg-Cu-W-Ag-Mo-Ba-F, in which As, Sb and Li are frontier elements, and F, Ba, Mo, W and F.
According to the research of Guilin Institute of Geology and Mineral Resources, the strong combination anomaly of gold, arsenic and adsorbed hydrocarbons (CH4, C2H6) is a favorable sign for gold prospecting evaluation.
5. Abnormal signs of geochemical exploration of copper-silver polymetallic deposits
According to the research of et al. (1995), the primary halo anomaly of Jilongding massive Cu-Ag polymetallic sulfide deposit in Rongxian county is very developed, and the zoning order of abnormal components from far to near is Ba (Mn)-As, Sb, Hg, Au-Ag, Pb, Zn, Cu-Ni, Co-Bi, Cd and Cd. Gold, mercury, antimony and arsenic are remote indicating elements, which are the combination of abnormal characteristics in the mine. Ag, Zn, Cu and Pb are near-ore anomaly combinations, while Cd and Bi only appear in the halo of massive sulfide ore bodies, which are ore-rich anomaly combinations. Secondly, the halo anomaly is characterized by the combined anomaly of Pb, As, Zn and Cu in the known ore body or ore belt, with regular anomaly, obvious zoning enrichment center, good anomaly coincidence and high anomaly content, and the internal halo scale is basically consistent with the ore body size. This abnormal feature of primary halo and secondary halo is a sign of prospecting evaluation of massive sulfide deposits in this area.
Fig. 7-2 Schematic diagram of iron and manganese zoning of Xika lazare deposit (according to овчиников, 1980).