6. 1. 1. 1 geological prospecting model
1) structural location: Halasu porphyry copper deposit is located in the Sawuer-Ertai island arc belt on the northern edge of Kazakhstan-Junggar microplate. There are Devonian island arc calc-alkaline volcanic rocks, Carboniferous continental acidic volcanic rocks and Permian intermediate-acidic volcanic rocks-molasse formation. The intrusive rocks in the middle Hercynian are mainly island arc granitoids. At the end of Carboniferous, it was a extensional environment. In Karatongke area, there are mafic-ultramafic complexes containing copper and nickel running through the fault.
2) Ore-bearing strata: Ore-bearing porphyry bodies intrude into the middle and lower lithologic members of Beitashan Formation of Middle Devonian, which are mainly intermediate-basic and basic volcanic rocks, mainly basalt, basaltic andesite and andesite, and mainly calc-alkaline volcanic rocks.
3) Ore-bearing rock mass: The ore-bearing porphyries are mainly intermediate-acid hypabyssal intrusive rocks, mainly granodiorite porphyry and granodiorite porphyry, with a small amount of contemporaneous porphyry. It is distributed along the fault and extends intermittently for about 7km.
4) Rock-controlling and ore-controlling structures: The distribution of ore-bearing porphyry bodies is controlled by the NW-trending Karashenger fault zone. The late mineralization is controlled by ductile shear zone, and the deformation structures include fold structure, schist structure/ductile shear zone, cleavage structure, sliding fault and low-angle reverse fault.
5) Ore body characteristics: Ore bodies are mainly produced in porphyry bodies and some in surrounding rocks. Irregular branching, expansion and contraction, branching compound and pinching along the strike and tilt directions.
6) Ore types and mineral combinations: the ores are oxidized ores and primary ores, mainly primary ores, with few oxidized ores. The ore minerals are mainly chalcopyrite, pyrite and magnetite, a small amount of bornite and molybdenite, and occasionally titanomagnetite and albite; The secondary oxidized minerals are malachite, followed by azurite, limonite and jarosite. Gangue minerals mainly include feldspar, quartz, biotite, sericite, chlorite, calcite and epidote. The associated beneficial elements in ore is gold, silver and molybdenum.
7) Ore structure: The ore structure mainly includes irregular granular structure, filling structure, nodular structure and fracture structure; Allomorphic-semi-automorphic granular structure is less. Ore structure includes disseminated mineralization in porphyry, skarn mineralization in the outer contact zone of porphyry, mineralization along schist zone and vein mineralization along fault.
8) Alteration types and zoning: The wall rock alteration mainly includes potash feldspar, silicification, sericitization, biotite, chloritization, epidote and carbonation. Alteration has obvious zonation in plane. From the center of the rock mass to the outside, the sequence is K feldspar silicified biotite belt-silicified sericite belt-chloritization epidote carbonate belt.
9) Ore-forming fluid: According to the H-O isotopic characteristics of fluid inclusions, it is considered that the ore-forming fluid comes from magma, indicating that the ore-forming fluid comes from the fluid differentiated in the late magmatism. From the S isotope analysis, it shows the characteristics of rich light sulfur isotopes, indicating that some minerals come from marine sedimentary strata.
10) metallogenic age: disseminated porphyry mineralization was formed in the middle Devonian, and vein-rich ore was formed by Triassic tectonic-hydrothermal superposition.
1 1) Genetic type: medium-low temperature porphyry copper deposit-structural superimposed porphyry copper deposit.
6. 1. 1.2 Geophysical and geochemical model
1) regional geophysics: the deposit is located in the wide gradient zone at the northern edge of the Jimunai-Ertaiba gravity anomaly area and the transition zone at the northern part of the Altai-Ertaiba positive magnetic anomaly area, with local magnetic anomalies developed.
2) Geophysical anomalies in the mining area: Mineralized bodies have high polarization characteristics (≥5%) according to the degree of mineralization. Most of the drilled rocks and ores have no magnetism or weak magnetism, while some of the amphibolite porphyries and altered basalts have strong magnetism, of which the former κ is 3883× 10-64πSI and Jr is1328×10-3a/m; The latter κ is 3782× 10-64πSI, and Jr is 34 1× 10-3A/m, indicating that the magnetism of rocks and minerals is obviously uneven. Therefore, the high polarization and relative high and low resistance of induced polarization method are important prospecting indicators to judge the distribution of sulfide ore bodies in this area. Exploration practice shows that high polarization and low resistance are often related to the distribution of carbonaceous layers.
Conventional induced polarization method and dual-frequency induced polarization method have been carried out in the mining area, and the abnormal reflection is consistent, which effectively reflects the distribution of ore-bearing geological bodies. Technical conditions are 1500m AB, 40mn, power supply period 8s, and delay 100ms. The background of polarizability in this area is less than 2%, and 4 anomalies are delineated with 3% as the lower limit of anomalies. Among them, there are three abnormal polarizabilities with peak values greater than 8%, corresponding to low resistivity, and the minimum value is less than 200 Ω m, which mainly reflects the distribution of carbonaceous sandstone. In the distribution area of porphyry copper deposits, the height of high polarization anomaly is 1000m and the width is 100 ~ 200 m, and the anomaly is not closed to the east. The polarization ratio is generally 3% ~ 5%, and the highest is 6.5%. Accordingly, the apparent resistivity is in the transition zone between high resistivity (1000 ~1400 Ω m) and relatively low resistivity (600 Ω m), while the low resistivity (≤ 200 Ω m) and high polarization in the northeast reflect the distribution of carbon-bearing strata. IP sounding shows that AB/2 has low polarization at 1.5 ~ 40m (1.5% ~ 2.5%), and the polarization rises sharply after 65m. When AB/2 reaches 500m, the polarization is above 5% and remains stable. The high polarization is in the transition zone from high resistance to relatively low resistance, and the high polarization anomaly has not been closed, indicating that the high polarization body extends downward greatly.
The change of magnetic field is complex, in which ore-bearing porphyries and mineralized bodies correspond to the change of background magnetic field, while adamellite in basic volcanic rocks shows obvious stable magnetic anomalies.
3) Regional geochemistry:1∶ 200,000 geochemical exploration is dominated by Cu and Au, accompanied by Ag, Cd, Mo, Sn, Cr, Ni, Co, MnO and other elements, and Pb is located in the northeast of the anomaly (Figure 6. 1). The abnormal shape is generally NW-SE with a total area of 96 km2, which is mainly located in the upper wall of Karashanger fault zone. The distribution of copper, gold, silver, molybdenum and tin is consistent and large, and the concentration center is obvious. Cr, Ni, Co and MnO are mainly in high background, and the abnormal distribution is relatively sporadic. The abnormal area of Cu is 68km2, with the highest value of 348× 10-6 and the average value of105×10-6. Au anomaly area is 28km2, with the highest value of 54. 1× 10 -9 and the average value of13.2x010-9. Molybdenum anomaly is mainly located in the center of copper anomaly, with the highest content of 4× 10 -6.
Fig. 6. 1 halasu copper mine1∶ 200,000 analysis chart
4) secondary halo anomaly in the mining area:1∶ 50,000 stream sediment survey hAs delineated obvious multi-element combination anomalies such as Cu, Au, Ag, Mo, W, Zn, As, Sb, Sn, Cr, Ni and Co, with an area of 10.7km2, in which Cu, Au, Ag, Mo and Co are included. The anomalies of chromium, nickel and cobalt and their high background are located in the intermediate-basic volcanic rocks of Beitashan Formation of Middle Devonian on the west side of the above anomalies. Pb shows no obvious abnormality (Figure 6.2). Among them, the Cu anomaly area is 6.8km2, the average value is 185× 10-6, and the highest value is 3438× 10-6. Au anomaly area is 2.3km2, with an average value of 35.6x10-9 and a maximum value of170x10-9. The abnormal area of molybdenum is 1km2, and the highest content is 14. 1× 10-6.
Fig. 6.2 geochemical profile of Halasu copper mine1∶ 50,000.
5) Anomaly of primary halo in mining area: There are obvious anomalies of combination of copper, molybdenum, gold and silver elements in rock geochemical survey. Its zoning features are as follows: copper, molybdenum and gold are in the inner zone, silver and antimony are in the middle zone, and arsenic, bismuth, lead, zinc, tin and tungsten are in the outer zone, which has the typical element combination characteristics of porphyry copper deposits.
The anomalies of Cu, Mo and Au are mainly located in the basalt of the upper and lower walls of ore-bearing porphyry bodies, and the enrichment centers of the three elements are consistent, and the * * * combination is obvious, mainly distributed in porphyry bodies. The abnormal length 1000 meters and the width are 300 ~ 600 meters, and the highest contents are 3326× 10-6, 12.5× 10-6 and196×/kloc-respectively.
Ag and Sb elements are mainly distributed in the upper and lower wall basalts of ore-bearing porphyry rock mass, and the enrichment center is mainly in the footwall, which is only a high background in the rock mass. Among them, the Ag anomaly is irregular ring with four concentrated centers, and its strike length is basically similar to that of porphyry, but they are all distributed in surrounding rocks, with the highest content of1266×10-6; Sb content is low and the background is high, and the highest content is only 0.36× 10-6.
As, Bi, Pb and Zn are mainly distributed in the high background and local anomalies in the outer contact zone of porphyry, and the general background in rock mass is low. Generally, the contents in rock mass are: Pb (8 ~ 10) × 10-6, Zn (40 ~ 80) × 10-6, As (2 ~ 5) × 10-6, Bi2O3. The concentrated distribution characteristics of the four elements in the contact zone are also inconsistent.
6. 1. 1.3 comprehensive prediction prospecting model
Based on the comprehensive analysis of the above geological prospecting model and geophysical and geochemical prospecting model, a comprehensive prediction prospecting model for the Halasu-Kalashenger porphyry copper belt is established, as shown in Table 6. 1
Table 6. 1 halasu porphyry copper deposit comprehensive prediction prospecting model