Delny Cu-Co deposit, Qinghai Province

Delny deposit is located in the southwest of Dawu Town, Maqin County, Guoluo Tibetan Autonomous Prefecture, Qinghai Province. It is a large deposit discovered according to people's reports.

I. Regional geological background

The mining area is located in the east of Anima Green Fold Belt of Bayankala Fold System, on the north side of the great fault in the southern margin of Qingshan Mountain in Anima, and in the middle of ultrabasic rock body in Delny in the direction of 300km NW or NWW.

The gravity Bouguer anomaly is a NW-trending cascade zone, and the field value increases from southwest to northeast with a gradient of about1×10-5m s-2/km. The magnetic field shows that under the calm background, the long axis is NW-trending, and elliptic δ T anomalies with different axis lengths are connected in a string (Figure 2.2. 1).

The geochemical anomaly zones of Cu, Co, Ni, Cr, Mn, Zn, Hg and other elements are distributed in NW-SE direction, reflecting the regional tectonic direction. Delny mining area is located in the southeast of the abnormal zone.

Second, the metallogenic geological environment

1. Strata

The exposed strata in this area are mainly Upper Paleozoic, followed by Mesozoic and Cenozoic.

The Upper Carboniferous (C3) is a monocline, which is banded in NW direction and inclined in NE direction. According to lithology, it is divided into four layers: amphibolite schist mixed with marble, marble, biolimestone and crystalline limestone, with gradual change of lithology. The Permian is widely distributed, and the Lower Permian is divided into two rock groups: ① the middle clastic rock zone volcanic rock group (P 1b) distributed in the middle and north of the mining area, which is composed of thousands of slates, carbonaceous slates and metamorphic sandstones, with volcanic lenses, and is the surrounding rock of ultrabasic rock bodies; ② The upper clastic rocks with carbonate rocks (P 1c) are mainly distributed in the south of the mining area. Upper Permian (P2) is mainly composed of limestone and sandstone.

The Middle-Lower Jurassic (J 1-2) is a set of coal-bearing clastic rocks, which belongs to faulted basin deposition. The Cretaceous (K) is exposed in the north of this area, with a large area, which is a set of purple conglomerate and glutenite. Tertiary (R) is a set of red clastic rocks, distributed intermittently along the fault zone in the middle of the region, with poor consolidation. Quaternary loose sediments are scattered in the valleys of the whole area.

2. Structure

The overall structural line in the area is consistent with the strike of strata, and the axial direction of fault zone, fold and long axis of rock mass is about 300 ~ 330.

(1) Fold: Delny anticlinorium, composed of lower Permian clastic rocks and volcanic rocks, with NW-SE axial direction; Along its axis, a series of NW-trending longitudinal faults, intrusions and Tertiary fault basins developed, forming a "fault intrusive rock belt". Cretaceous fault basin, distributed along the direction of 120 ~ 130, is more than 30 kilometers long and 4 ~ 6 kilometers wide, which is actually a syncline structure.

(2) Faults: concentrated in anticlinorium of Delny, which can be divided into three groups: NW-trending longitudinal faults, NE-trending transverse faults and nearly EW-trending oblique faults. Among them, NW-trending faults appear in dense zones, which run through the whole area and consist of a series of faults inclined to NE, with the characteristics of multi-stage activity; NNE-trending small-scale faults; The nearly east-west faults are a group of concealed structures, which reflect the basement structure in this area.

Fig. 2.2. 1 Geophysical field analysis map of Delny deposit and its periphery in Qinghai.

3. Magmatic rocks

The magmatic activity in the area is strong and magmatic rocks are developed, which are divided into ultrabasic rocks and acidic intrusive rocks, which are NW-SE banded and mainly distributed in the middle of the mining area. Together with the longitudinal fault, a fault-magmatic rock belt with a width of about 3 ~ 5 kilometers is formed.

(1) ultrabasic rocks: A series of rocks with different sizes constitute ultrabasic rock zones. The largest ultrabasic rock mass in Delny is about 17km long and1km wide. It can be divided into four small rock areas. The rock types are mainly pyroxenite, followed by peridotite, pyroxenite and a small amount of gabbro. The alteration is strong, mainly serpentine. Except gabbro, the rocks are serpentine and carbonate serpentine.

Delny copper-cobalt deposits are related to ultrabasic rocks and strictly controlled by ultrabasic rocks, and almost all ore bodies occur in ultrabasic rocks. The larger the rock mass, the more favorable the mineralization is.

(2) Acidic intrusive rocks: distributed in the northern part of ultrabasic rock belt, with large and small rock bodies exposed intensively, forming an acidic intrusive rock belt, mainly granite, and the rest are granodiorite, amphibole granite, granite syenite and so on. All of them are small rock masses with small scale and less exposure.

4. Regional geochemical field

(1) The average contents of trace elements in some strata and magmatic rocks are shown in Table 2.2. 1 and Table 2.2.2.

Table 2.2. 1 Trace Element Content in Formation

Table 2.2.2 Contents of Trace Elements in Some Magmatic Rocks

① The contents of Cu, Co and Zn in amphibolite schist of Upper Carboniferous and basic volcanic lava of Lower Permian are obviously higher than those in other rocks; Content of clastic rocks (sandstone, slate, etc.). ) Pb is the highest below Permian; The element content of marble in Upper Carboniferous is the lowest among all rocks.

② The contents of Co, Zn, Cr and Ni in ultrabasic rocks are the highest, which are 79× 10-6, 13× 10-6, 1347× 10-6 and 65438 respectively. Copper content is the highest in quartz diorite, and lead content is the highest in quartz diorite and porphyritic biotite granite.

(2) Regional geochemical anomalies

1∶ 200,000 drainage system sediment survey anomaly shows (attached figure 2.2.2), and the concentration center of Cu anomaly is clear, which obviously corresponds to Delny deposit. See Table 2.2.3 for the characteristic parameters of its main components.

Fig. 2.2.2 Anatomical map of regional geochemical anomalies of Delny deposit in Qinghai.

Table 2.2.3 Summary of Regional Geochemical Anomaly of Delny Deposit

5. Regional geophysical field

Delny deposit is located in the northwest-southeast gravity gradient zone.

Aeromagnetic δ T anomaly corresponding to ultrabasic rocks; About 24km long and 6 km wide; δTmax≈ 120 nt, and the northeast δTmin ≈- 20nT negative anomaly. The controlled geomagnetic δ z anomaly is intermittent from west to east for 50km, with a steep gradient, less than 3km at the widest point and only100m at the narrowest point. The intensity is n× 100 ~ 7000 nt, and the north side is sometimes accompanied by negative anomalies. The magnetic field on the south side is about 150nT higher than that on the north side.

Three. Geological characteristics of ore bodies

1. Combined distribution and occurrence of ore bodies

By the end of 1990, * * has identified 5 main ore bodies (serial numbers: Ⅰ, Ⅱ, Ⅲ, ⅴ, ⅶ) and 29 subsidiary ore bodies, forming 5 ore bodies. The ore body is layered or lenticular, and it is obviously folded due to the influence of late structure. The extension along the strike is relatively stable, the main ore body fluctuates, and the overall tendency is eastward. All ores are produced in ultrabasic rocks, with clear boundaries with surrounding rocks, but except ultrabasic rocks, the roof part is sandstone.

2. Ore structure and main mineral assemblage

The ore structures are mainly massive, disseminated and banded, followed by veins, reticulate veins, spots and spots.

The main metal minerals are pyrite and pyrrhotite, followed by chalcopyrite, sphalerite and magnetite. And a small amount of chromite spinel, white iron ore, cobalt-nickel pyrite, bornite, celestite, malachite and so on. The metallic minerals in oxidized ores are goethite, goethite and hydrohematite. Non-metallic minerals are mainly calcite and dolomite, followed by timely and talc.

3. Mineralization stage and zoning

The genesis of Delny deposit is complex, and it is a multi-stage, multi-genesis and multi-mineralization compound superimposed deposit. Its formation has gone through five stages.

(1) magmatic differentiation stage: it is the main metallogenic stage of Delny deposit, and the Cu-Co (S, Zn) ore bodies in ultrabasic rocks are formed by crystallization differentiation and magmatic detachment.

(2) Rock mass emplacement stage: it has a certain transformation effect on the initially formed ore body, resulting in new small ore bodies.

(3) Structural transformation stage: only the shape and occurrence of ore bodies are changed.

(4) Hydrothermal superposition stage: the ore body is reformed again, and at the same time, late pyrite, chalcopyrite and magnetite are generated, most of which are veinlets interspersed with the original ore.

(5) Superficial stage: forming iron cap, etc.

Mineralization zoning is not obvious. Pyrite and chalcopyrite are evenly distributed in the ore body, but sphalerite is mostly distributed in the upper part of the ore body, and pyrrhotite is distributed in the edge of the ore body.

4. Types and distribution of alteration

Ultrabasic rocks are the surrounding rocks of ore bodies, with developed alteration, serpentine and carbonate rocks are the most widely distributed, which have a certain spatial relationship with ore bodies and have certain prospecting significance. Followed by slip petrochemical, chloritization, sodium flash petrochemical, silicification, epidotization, biotite and so on. Alteration is weak, not widely distributed and not closely related to ore bodies.

5. Oxidation zone

Iron hat and limonite formed under supergene action, and iron breccia formed by some Quaternary residues cemented by iron are distributed in a large area. Near the top of shallow-buried ore body, the terrain is characterized by subsidence.

6. Main ore-controlling factors

Ultrabasic rocks are the basic factors of ore control. The formation of early primitive magmatic deposits is related to magnesium-rich ultrabasic rocks; Ultrabasic rocks are ore-forming parent rocks and surrounding rocks of ore bodies.

Primitive magma rich in sulfur and sulfur-loving elements is the main ore-controlling factor for the formation of molten deposits.

The fault structure controls the distribution of ultrabasic rocks, so the deep fault zone is an extremely important indirect controlling factor for the formation of ore bodies.

Carbonated alteration is closely related to ore bodies, and has a certain control effect on the formation of ore bodies.

Four. Geophysical characteristics of mining area

1. Physical properties of rocks and ores

Table 2.2.4 summarizes the physical properties of main rocks and ores in this area by reference.

When sorting out the physical data comprehensively, the magnetic susceptibility and residual magnetization of the non-magnetic samples listed in the original data are given as κ: 10× 4 π× 10-6Si and MR: 50× 10-3a m- 1 respectively according to their minimum measured values, so as to make statistics again.

The measured data of samples with power supply time of 1 min in the original data are selected for the polarizability and resistivity. The measured value of resistivity is higher than the actual value under natural conditions, but the polarizability may be lower.

Table 2.2.4 Table of Physical Parameters of Main Rocks and Minerals in Delny Mining Area

2. Physical model

According to the physical characteristics of the main geological bodies in the mining area summarized in Table 2.2.4 (Table 2.2.5), it can be seen that the physical differences between rocks and ores in the area are extremely obvious or obvious; The physical properties of main geological bodies can be compensated by parameters, which provides a good physical premise for comprehensive geophysical exploration methods.

3. Geophysical anomalies

According to the geophysical comprehensive plan of the main ore body distribution area and the comprehensive profile of 13 and 15 exploration lines, the effect analysis is as follows.

Table 2.2.5 Physical Properties of Main Geological Bodies in Delny Mining Area

(1) gravity

The density difference between ore and surrounding rock is large, which provides excellent physical properties for gravity exploration. The gravity plan (Figure 2.2.3) compiled from the data of several gravity survey lines shows that the buried depth is less than 50m, and the local anomaly of 1 ore body is obvious and the occurrence is gentle. The large gravity anomaly in the south (length 1 100 m, width 600 m) corresponds to the Lower Permian (P 1) stratum, in which ultrabasic rock belts are distributed.

On the profile of 13 exploration line, the gravity anomaly amplitude after land reform and regional correction reaches1.8×10-5m s-2, and the maximum value corresponds to the convex part of the ore body (Figure 2.2.4); The gravity anomaly amplitude of the exploration line15m away from it reaches 3.2×10-5m s-2 (attached figure 2.2.5). The gravity anomaly in the southern section of 13 line is caused by high-density andesite exposed locally. It shows that andesite may form gravity interference anomaly.

(2) Ground magnetic survey

The intensity of magnetic anomalies in the area is high and varies greatly, mainly positive anomalies, and there are weak or negative magnetic anomaly zones in the north and south, where the δ z is as high as 2000 ~ 5000 nt, and the δ z local anomaly is less than -500nT. The southern edge of the positive anomaly basically corresponds to the southern boundary of the ultrabasic rock body in the northern zone, and the middle low weak magnetic anomaly zone is related to the decrease of carbonate alteration magnetism near the mine. The southern part is a negative anomaly with a local intensity less than-2000 nt; It is estimated that it is related to the fact that the lower boundary of the rock mass in the northern belt leans northward and the extension of the rock mass in the southern belt is limited.

On the profile, the abnormal gradient of rock mass in the northern belt is steep, and the positive and negative abnormal intensities are about 3000nT and -400nT respectively, which corresponds well with the rock mass boundary. The rock mass in the southern belt is not obvious.

(3) Electrical methods

① Abnormal self-electricity: wide range and regular shape. The -80mV δ U isoline is closed in an oval shape, with a length of about 1.3km and a width of about 0.6km, which is consistent with the distribution of ore belts. The closed circle contains seven local anomalies, the amplitude of which is-160 ~-320 mv, mainly in the northwest. They all fall within the projection range of the known ore body surface, reflecting the shallow ore bodies with good redox conditions. Because the groundwater level in this area is shallow, it does not reflect well on deeper ore bodies. Although the abnormal shapes of DZ-3 and 12 on the south side of the ore anomaly are similar to those of the ore anomaly, they are non-ore carbonaceous slate anomalies because there is no magnetic anomaly and they are located in the distribution area of carbonaceous slate.

Figure 2.2.3 Comprehensive Geophysical Plan of Main Ore Bodies Distribution Area of Delny Deposit

Figure 2.2.4 Comprehensive Geophysical Profile of Main Ore Body Distribution Area 13 Exploration Line of Delny Deposit.

Figure 2.2.5 Comprehensive Geophysical and Geochemical Exploration Profile of Delny Main Ore Body Distribution Area 15 Exploration Line

On the profile, between 180 ~ 205, the self-electricity anomaly is steep in the north and slow in the south, with the intensity of -270 mv, corresponding to the near-surface 1 ore body; The anomaly near 250 is a disturbance anomaly caused by carbonaceous slate.

② Transient electromagnetic method: 13 line test results show that large, shallow and rich ore bodies reflect well, and there are obvious anomalies in each time channel; But there are similar anomalies on carbonaceous slate. Therefore, it is difficult to distinguish ore-bearing and non-ore-bearing anomalies by transient electromagnetic method alone.

③ induced polarization method: the effect is not good, the high background range of η s > 15% accounts for 80%, and the highest anomaly is in the southern carbonaceous slate distribution area. As the occurrence of ore bodies is gentle, overlapping and disturbed by carbonaceous slate, the anomalies on the ore bodies are not obvious (Figure 2.2.5). According to the existing data, it is still difficult to delineate ore bodies and ore belts according to IP anomalies.

④ Charging mode: Figure 2.2.6 shows that the charging mode in Delny mining area has played an important role. (a) Ore body boundaries can be delineated according to inflection points in gradient curves (Figure 2.2.5); (b) Adjacent blind ore bodies can be found; (c) In the case of overlapping ore bodies and complicated shapes, the basic shapes and connection relations of ore bodies can be determined with the help of prospecting engineering.

4. Interference body or interference factor and its influence

High density andesite and tuff may be the interference of gravity anomaly of ore body; Graphite-bearing or carbonaceous slate and schist are the main interferences in electrical and electromagnetic exploration.

Verb (abbreviation of verb) geochemical characteristics of mining area

1. Geochemical parameters of rocks and ores

Table 2.2.6 shows the contents of trace elements in several rocks mainly exposed in the mining area, among which the average contents of Cu and Zn in ultrabasic rocks are the highest and the coefficient of variation is also large; The ultrabasic rocks have the highest contents of Co, Ni, Cr and Au, and the ratio of w(Ni)/w(Co) is 12.97.

Table 2.2.6 Geochemical Parameters of Main Surrounding Rock of Delny Deposit

Table 2.2.7 gives the average contents of ore-forming element Co and associated trace elements in the ore, indicating that the contents of Co, Au, In and Ni in the lower ore body are higher than those in the upper ore body; The ratio of tungsten (nickel)/tungsten (cobalt) is 0. 12 ~ 0.45. Compared with the average chemical composition of peridotite In China, Se in ore is nearly 500 times higher, and Tl and In are about 50 times higher. Low Pt and Pd;

In addition, according to other data, the w(Ni)/w(Co) ratio of ultrabasic rocks is 10 ~ 20, and the maximum value is 37.5. The ratio of w(Ni)/w(Co) of ultrabasic rocks in the roof and floor of ore bodies is obviously reduced to 3.3 ~ 8.0.

Table 2.2.7 Average content of associated components in main ore bodies of Delny deposit.

Fig. 2.2.6 Comparison between the boundary inferred by charging method of No.Ⅰ ore body and the boundary delineated by exploration engineering.

2. Geochemical anomalies

(1) River system sediment measurement: A large area of copper anomaly consisting of multiple concentration centers appeared in the river system sediment measurement of the mining area and its periphery 1∶50000 (Figure 2.2.7), with clear concentration zoning. W(Cu)=60× 10-6 trap anomaly is about18km2; ; The anomaly of trap W(Cu)= 100× 10-6 is about 2.5km2, and Delny copper mine is located in the trap w(Cu)= 150× 10-6.

(2) Soil survey (1∶ 1 000): The mining area is circled with anomalies of elements such as Cu, Zn, Co, Au and Hg, and their respective enrichment centers are formed near the exposed parts of the ore body (Figure 2.2.8). Among them, the anomaly range of Cu is the largest, with obvious concentration zoning, and the anomaly area is about 0.03km2, where w(Cu)=40/ 10-6. The abnormal range of zinc, cobalt and mercury is small; W(Au)= 1.5× 10-9, and the anomaly range is similar to that of Cu.

Fig. 2.2.7 Cu anomaly map of1∶ 50,000 drainage sediments in Delny mining area and its periphery.

At the 1 ore body, Cu anomaly appears below the outcrop of the ore body, with extremely narrow anomaly and steep peak value (Figure 2.2.5), which shows the supergene geochemical characteristics of physical weathering and small or undeveloped secondary halo diffusion distance in alpine mountain areas.

(3) Rock survey: Only sporadic samples are collected, and it is found that the anomalies of elements such as Cu, Pb, Zn, Cr, Ni, Co, V and Ti only appear in the ore body, and there are no anomalies when leaving the ore body.

3. Elemental zoning sequence and evaluation index of mineralization and denudation degree.

There is no study on the element zoning sequence in this area. The relationship between anomalies and minerals and ultrabasic rocks can be judged by the ratio of w(Ni)/w(Co): the ratio of w(Ni)/w(Co) in general ultrabasic rocks is10 ~ 20; The w(Ni)/w(Co) ratio of ultrabasic rocks near the mining area is 3 ~ 8. W (Ni)/W (Co) near ore body <1.

Geological geophysical geochemical prospecting model of intransitive verb

1. Table 2.2.8 summarizes the geological-geophysical-geochemical prospecting indicators of Delny copper-cobalt deposits.

2. See Figure 2.2.9 for the geological-geophysical-geochemical prospecting model of Delny copper-cobalt deposit.

3. Combination process of geophysical and geochemical exploration optimization methods in geological exploration.

Delineation of (1) ultrabasic rock belt:1∶ 200,000 area gravity and aeromagnetic survey are the main methods.

(2) Identification of ore-bearing rock mass: 1∶65438+ 10,000 ~1∶ 50,000, gravity and magnetic exploration and river sediment investigation.

Fig. 2.2.8 Geochemical anomaly map of soil measurement of Delny deposit 1 orebody.

Figure 2.2.9 Geological-Geophysical-(Geochemical) Prospecting Model of Delny Copper-Cobalt Deposit

Table 2.2.8 Geological-Geophysical-Geochemical Prospecting Indicator Set of Delny Deposit

Table 2.2.9 Parameter Table for Forward Calculation of Physical Geological Body and Gravity and Magnetic Anomaly in Delny Deposit

(3) Delineate the general part of the ore body:1:25,000 ~1:10,000, with medium and high precision gravity and magnetic exploration and comprehensive electromagnetic exploration mainly based on electromagnetic sounding.

Seven. Brief table of geological, geophysical and geochemical characteristics

Table 2.2. Summary of geological characteristics of copper-cobalt deposits in Delny.

Table 2.2.B Overview of geophysical characteristics of copper-cobalt deposits in Delny.

Table 2.2.C Summary of geochemical characteristics of copper-cobalt deposits in Delny.

Table 2.2. Summary of Geological Characteristics of Copper-Cobalt Deposits in Delny

Table 2.2.B Overview of Geophysical Characteristics of Delny Copper-Cobalt Deposit

Table 2.2.C Overview of geochemical characteristics of copper-cobalt deposits in Delny.