The mineralization type of the Xiaoxinanfork deposit is relatively special, and it is one of the few large porphyry copper-gold deposits that have been discovered in China. Medium stripping intensity, the geochemical landscape is the forest-covered area in eastern Jilin.

3.2.2.1 Regional Geological Environment of the Mineral Field

The geotectonic position is located in the Yanbian Fold System of Xing'an-Nemeng Trough Zone of the Pacific Rim metallogenic domain.

The tectonic magmatic activity in the area is strong, NNE to the Sandougou-Xiaonanfork tectonic fragmentation belt through the area, near the SN to the NW, NW, NNW to the fracture is also more developed. NNE to the fracture of the NW to the fracture is the main ore-holding tectonics. Magmatic rocks are exposed in large areas, mainly granodiorite, dioritic granite and granodiorite, in addition to gabbro and diorite. The diorite ( ) small rock body in the early Yanshan period is most closely related to mineralization (Figure 3-2-4).

Figure 3-2-3 Regional geological and geochemical anomaly structure pattern of Dexing Cu-Mo mine field in Jiangxi

The outcrops in this area are relatively simple, dominated by sandstones, siltstones, volcanic tuffs, and slates sandwiched with marble lenses of the Permian system, and gneisses, schists, and hornblende sandwiched with graywacke lenses of the Pz system, with the latter being the ore-endowed stratigraphy.

Figure 3-2-4 Geological sketch map of the Little Southwest Fork Copper and Gold Ore Field, Jilin (simplified from 1:200,000 geologic map of Hunchun and Chunhua in Jilin Province)

1-Quaternary system; 2-basalt, olivine basalt; 3-conglomerate, sandstone; 4-moderate acidic felsic rocks and tuffs; 5-moderate acidic felsic rocks and tuffs. -medium acidic lava and tuff; 5-sandstone, siltstone, volcanic tuff; 6-gneiss, gneiss, hornblende sandwiched with graywacke; 7-granitic diorite; 8-granodiorite; 9 plagioclase granite; 10-quartz diorite; 11-amphibolite; 12-plagioclase; 13-fault/fracture zone; 14-geologic boundary; 15-mineral deposit

The multi-element anomaly combinations related to mineralization in this field are classified as follows:

(1) Mineralization element anomaly combination: Cu-Au.

(2) Indicator element anomaly combinations:

1) Direct indicator anomaly combination Cu-Au-Ag;

2) Indirect indicator anomaly combination As-Au-Ag; and Indirect indicator element anomaly combination As-Sb-Hg, W-Mo-Bi;

(3) Mineralization environment element anomaly combination: Ni-Cr-Mg, Si-Al-Nb-Be.

1) Characteristics of anomalous distribution of mineralization elements

Based on the special mineralization type of this deposit, Cu and Au are the main mineralization elements in this field. Their multi-element positive anomalies are distributed above the known ore field, with clear concentration zones, and the known deposit is located in the inner zone of the anomaly. The anomalies are saddle-shaped and distributed in the near NEE direction above the mineralized rock bodies and mineralized strata, and the Cu-Au combined anomalies are mostly negative or absent in the non-mineralized rock bodies in the region. This also indicates that the positive anomalies above the ore field are due to mineralization (Figure 3-2-5).

2) Characteristics of the distribution of indicator element anomalies

(1) Characteristics of the distribution of direct indicator element anomalies

Cu, Au, and Ag are the mineralizing elements and associated elements of the deposit, and their multi-element positive anomalies are similar to the Cu-Au anomalies in their morphology and distribution, which enclose the known mineralizing rocks and surrounding rocks, and there is a clear anomalous concentration center above the deposit. The anomalies are distributed in the near NEE direction, indicating that they are influenced by the east-west tectonic structure and have a large area. The above features indicate that this group of multi-element anomalies is controlled by tectonics, closely related to mineralization, and can be regarded as ore field anomalies, which directly indicate the existence of mineralization. There is a small area of negative anomalies distributed in the south of the ore field anomalies (Figure 3-2-5).

(2) Distribution characteristics of indirect elemental anomalies

① As-Sb-Hg

The multi-elemental positive anomalies are distributed along the NNE fracture above the Pz stratum and its contact zone with the rock body, with a large area, which is mainly controlled by the near-north-south tectonics, resulting in the distribution of the anomalies in a south-north direction, and there are two centers of concentration, and the one in the northern section overlaps with that in the mine field and surrounds known ore deposits and mineralized rocks. There are two centers of concentration in the northern section, which overlap with the anomalies of the ore field and enclose the known ore deposits and ore-forming host rocks, so it can play a certain role in indicating the mineralization (Figure 3-2-5).

② W-Mo-Bi

is an indicator element for a set of high-temperature hydrothermal fluids. The distribution has two sets of anomalies, east-west oriented and northwest oriented. The main body of the east-west anomaly is located in a large granite body, which partially overlaps with the ore field anomaly, and the known deposits are at the edge of this anomaly, overlapping with the ore field anomaly. The north-south anomaly overlaps with the As-Sb-Hg positive anomaly, and is spatially unrelated to the known minefield anomaly along the NNE tectonic distribution above the Pz formation and its contact zone with the rock body (Figure 3-2-5).

The occurrence of As-Sb-Hg and W-Mo-Bi positive anomalies can be combined with direct indicator elements to indicate the presence of mineralization.

3) Characteristics of the distribution of elemental anomalies in the mineralizing environment

(1) Ni-Cr-Mg

Their positive anomalies appear on the known ore fields and surround the known ore deposits and mineralizing rock bodies. The distribution location overlaps with that of the ore field anomalies, and the anomalies of the two are highly superimposed. The range is smaller than the ore field anomalies. The elemental positive anomalies of this group are distributed in the mineralized stratum and its contact zone with the rock body within the ore field, while they do not appear on the same stratum in the region. This indicates that their formation is related to mineralization (Figure 3-2-5).

(2) Si-Al-Nb-Be

Negative anomalies occur above the ore field, nested with the ore field anomalies, encircling the ore-bearing rock body and the known deposits, with an EW strike. Regionally, negative anomalies for elements in this group generally occur above the stratigraphy, while positive anomalies are generally located above the rock body (Figure 3-2-5). Therefore, negative anomalies occurring above the deposits reflect a certain metallogenic environment and are associated with mineralization. Reflecting the iron-rich and alkali-poor mineralization process.

3.2.2.3 Structural pattern of geological and geochemical anomalies in the ore field

(1) Structural pattern of regional geological features in the ore field

Constrained by deep and large fractures, it is located in the intersection part of several sets of fractures, and is intruded by diorite mélange body in the early Yanshan period. The deposit is mainly located in the mafic body, and the ore-endowed strata are schist, gneiss and hornblende strata of Pz (Figure 3-2-6).

Figure 3-2-5 Multi-element anomaly map of the Xiaonanquan mine field

(2) Structural pattern of regional geochemical anomalies in the mine field

Under the favorable geological environment for mineralization mentioned above, there is a large range of multi-elemental positive anomalies (mine field anomalies) of Cu-Au-Ag with obvious concentrations, and there are also positive anomalies of indirectly indicative elements, such as As-Sb-Hg and W-Mo-Bi, occurring within the mine field anomalies. Positive anomalies of As-Sb-Hg, W-Mo-Bi, and indirect indicator elements occur within the mine field anomalies. Ni-Cr-Mg, which reflects the mineralization environment, appears positive above the mine, while Si-Al-Nb-Be appears negative, both of which are well integrated with the mine anomalies. There is a small area of negative Cu-Au-Ag anomalies in the periphery of the ore field anomalies. The spatial distribution of mineralization anomalies is centered on the positive anomalies of mineralization elements and associated elements, with other groups of multi-element anomalies overlapping or integrating with them (Figure 3-2-6).

Figure 3-2-6 Regional geogeochemical anomaly structure pattern of the Xiaonanfo Cu-Au field in Jilin