1 metallogenic geological background
Laizhou Sizhuang mining area is located in the south section of Jiaojia metallogenic belt, and the exposed strata in the area are Quaternary Holocene loose sediments. The distribution of bedrock is bounded by the main fracture surface, with Neoproterozoic Sinian Linglong adamellite in the east and Malianzhuang gabbro and Linglong adamellite in the west (north of Sizhuang).
The distribution and intensity of gold mineralization in the mining area are controlled by structural faults, and the ore body output is controlled by Jiaozhujia fault and Sizhuang ①, ② and ③ secondary branch faults (Figure 1). The Jiaojiazhu fault in Sizhuang mining area is about 4km long, 80 ~ 500 m wide and 1 140m deep. On the plane or section, it extends in gentle waves, with strike of 325 ~15, NW or SW, and dip angle of 30 ~ 45.
The main fault (north of Sizhuang) is distributed along the contact zone between Malianzhuang gabbro and Linglong adamellite, and south of Sizhuang is developed in Linglong adamellite. Linglong adamellite develops secondary branch faults and joint dense zones.
Figure 1 Geological Schematic Diagram of Sizhuang Gold Mining Area in Laizhou City
1-Quaternary sandy clay; 2- Neoarchean Wutai-Fuping metamorphic gabbro; 3- Neoproterozoic Linglong adamellite; 4- pyrite sericitized granite; 5- pyrite sericitized granite cataclastic rock; 6- pyrite sericite cataclastic rock; 7- Woven dacite granite; 8- K granite; 9— Gold ore body; 10-main fracture surface and occurrence; 1 1- location of gold deposit
2 Geological characteristics of ore bodies
2. 1 characteristics of ore bodies
Gold mineralization is mainly distributed below the main fracture surface. The ore bodies of 1, No.2 and No.3 are the same as or roughly parallel to the main fracture surface, and the main ore bodies are inclined in the south-west direction.
2.1.1I ore body group
The 1 ore body group is composed of 14 ore body, and its resources account for 40.75% of the total (of which 1- 1 main ore body accounts for 39.39% of the total). The ore bodies are controlled by the main fault alteration zone and distributed between-926 and -926 ~-240 m in the elevation of line 254 ~ 362 in the mining area. Strike 2 ~ 30, dip SW or NW, dip 21~ 41; The controlled strike is 60 ~ 480 m long, the controlled dip is 50 ~ 369 m deep, and the true thickness of the ore body is 0.87 ~ 23.82 m; Gold grade is1.16×10-6 ~ 5.46×10-6. The ore bodies are vein-like, short-vein-like and lenticular, and occur in the sericitized fractured rock zone of pyrite, with disseminated mineralization as the main factor, followed by vein-like mineralization.
2.1.2 Ⅱ ore body group
Ore body group ⅱ consists of 28 ore bodies, and its resources account for 1.36% of the total resources. The ore bodies are controlled by the alteration zone of the main fault, distributed between -920 ~- 159 m along the line 254 ~ 362 in the mining area, with strike of 0 ~ 8, dip of W or NW, dip angle of 21~ 34, control length of 60 ~ 2 10 m and control depth of 50 ~. The ore body is short vein and lenticular, and occurs in the fractured rock zone of pyrite sericitized granite. The main mineralization is star-shaped and veinlets, followed by massive mineralization.
2.1.3 Ⅲ ore body group
Ore body group ⅲ is composed of ore body 146, and its resources account for 57.89% of the total resources (of which the resources of main ore bodies ⅲ- 1 and ⅲ-2 account for 28.64% of the total resources). The ore bodies are controlled by Sizhuang main fault zone and secondary branch faults ①, ② and ③, distributed between the elevation of line 252 ~ 378-1003 ~-235 m, with strike of 342 ~ 28, dip of SW or NW, dip angle of 23 ~ 47, controlled length of 60 ~ 905 m and controlled depth of 50 ~ 50m. The ore bodies are vein-shaped, short-vein-shaped and lenticular, and occur in pyrite sericite granite cataclastic rocks in the pyrite sericite granite belt, with vein mineralization as the main factor, followed by star-shaped and massive mineralization.
2.2 Characteristics of main ore bodies
2.2.1Ⅰ-1ore body
Ore body resource reserves account for 39.39% of the total reserves, and are distributed between -926 ~-32 1m elevation 248 ~ 280. Ore bodies occur in pyrite sericitized cataclastic rocks (local pyrite sericitized granitic cataclastic rocks) 0 ~ 36 m below the main fracture surface, and are distributed in layers. Along the strike and dip, there are obvious soothing waves, branching and compounding, expansion and contraction.
The occurrence of ore body is consistent with the main fracture surface, with strike 17 ~ 24, average 20, dip NW, dip angle 27 ~ 35, and average dip angle 3 1. The control strike length of this project is 480m, the control dip depth is 202 ~1192m, and the average dip depth is 772m. ..
The thickness of ore bodies in a single project is 1.53 ~ 23.82 m, with an average of10.40m. Most of them are 10.39 ~ 23.82 m, accounting for 56%. In addition, 25% is 2.82 ~ 8.64 m, and 10 is less than 2.50m m. From the profile, it can be seen that the thickness of two ore bodies is large and the middle is thin along the dip, and the thickness variation coefficient is 63%, which is a stable ore body with thickness variation.
The gold grade of a single project is1.2/kloc-0 /×10-6 ~ 5.46×10-6, with an average of 3.03× 10-6. Among them, 2.62×10-6 ~ 5.46×10-6 is the majority, accounting for 69%, and1.00×10-6 ~ 2.5×10-6 accounts for 3/. The grade varies unevenly along the dip, and the high value is distributed in the middle and lower part of Line 264, with a grade variation coefficient of 83%, which belongs to the ore body with uniform distribution of useful components.
The ore body is controlled by the structure before and during mineralization, and the mineralization intensity is related to the degree of fault development. The lithologic section with developed fractures has a high gold grade, and the thickness is slightly inversely proportional to the grade, and the ore body boundary shape is regular.
2.2.2 Ⅲ-2 orebody
The ore body resource reserves account for 17.46% of the total reserves, and are distributed between the 264 ~ 328 lines at an altitude of-760 ~-235 m. The ore body occurs in the pyrite sericite granite cataclastic rock in the pyrite sericite granite belt below the main fracture surface 185 ~ 3 15m. Strictly controlled by the occurrence of the floor in the main alteration zone, it spreads in gentle waves along the strike and dip, and has the characteristics of branching and compounding, expansion and contraction, and pinching and reappearing. The ore body strike is 345 ~ 36, with an average of14, dipping towards SW or NW, and the dip angle is 26 ~ 45, with an average of 35. The control strike length of this project is 905m, the control dip depth is 85 ~ 672m, and the average dip depth is 342m. ..
The thickness of single engineering ore body is 1. 18 ~ 8.58 m, with an average of 3.46m, of which 2.4 1 ~ 4.88 m accounts for 46%. 1.18 ~1.46m accounts for 38%. From Line 304, it gradually becomes thinner to both sides along the strike, and the thickness variation coefficient is 7 1%, which is a stable thickness variation ore body.
The gold grade of a single project is1.52×10-6 ~17.20×10-6, with an average of 7. 10× 10-6 and 2.50×. It belongs to the ore body with uniform distribution of useful components.
The ore body is controlled by the structure before and during mineralization, and the mineralization intensity is related to the degree of fault development. The lithologic section with developed fractures has a high grade of gold, and the mineralization is characterized by micro-discontinuity, with a positive fluctuation relationship between thickness and grade, and the shape of ore body boundary is regular (Figure 2).
Fig. 2 Geological Profile of No.264 Exploration Line in Sizhuang Gold Mine Area, Laizhou
Q— Quaternary sandy clay; V- metamorphic gabbro; η γ adamellite; γJH- pyrite sericitized granite; SγJH- pyrite sericitized granite cataclastic rock; SJH-pyrite sericitized cataclastic rock;
1- gold ore body and its number; 2-main fracture surface; 3— Drilling position
3 ore characteristics
3. 1 Mineral composition
Ore minerals mainly include silver-gold ore, gold-silver ore, pyrite, galena and sphalerite. Gangue minerals mainly include quartz, sericite, feldspar and calcite.
The beneficial component in the ore is mainly gold. Followed by associated beneficial components Ag and S. The average grade of Ag in the deposit is 5.06× 10-6, and the average content of S is 2.26%, which can be comprehensively recovered as associated beneficial components.
3.2 Ore structure
The ore structure is mainly granular structure, followed by cataclastic structure, interstitial structure, inclusion structure, metasomatic residual structure, metasomatic false structure, graphic structure and emulsion structure.
Ore structures are mainly disseminated, veined, veined and dotted structures, followed by breccia and staggered veined structures.
3.3 Ore types
3.3. 1 natural type
According to the mining data, the depth of oxidation zone is 35 ~ 40m, the depth of mixed zone is-15m, and the buried depth of middle and deep ore bodies is-1000 ~-300m. The natural type of ore is primary ore. According to the mineral composition, texture, alteration and crushing degree of ores, primary ores can be divided into three types. The first group of ore bodies are mainly disseminated pyrite sericitized cataclastic rocks; Vein disseminated pyrite sericitized granite cataclastic type ore is the main type of orebody ⅱ and orebody ⅲ. Vein network vein pyrite sericitized granite type ore is the secondary type of No.3 ore body group.
3.3.2 Types of ore industry
The content of harmful elements such as arsenic (0.002 1%) in the ore is low, and the sulfur content is 2.26%. The ore belongs to low sulfur gold ore.
3.4 Characteristics of Gold and Silver Minerals
3.4. 1 gold minerals
Gold minerals are mainly intergranular gold (49.87%), fissure gold (42.8 1%) and a small amount of inclusion gold. Gold minerals are mainly fine-grained gold (66.67%), followed by fine-grained gold (32.79%), with a small amount of medium-grained gold. The forms of gold minerals are mainly angular (26.29%), granular (16.80%), dendritic (15.99%), rectangular (13.0 1%) and round (65438+).
The gold minerals in the ore belong to the series of gold and silver minerals, with silver and gold ores as the main minerals, followed by gold and silver ores. The highest fineness of gold minerals is 776, the lowest fineness is 295 and the average fineness is 532.25. The fineness of gold in Sizhuang Gold Mine (average 532.25) is mainly low, which is lower than that in Jiaojia Gold Mine (average 670.07).
Silver mineral
Silver minerals are mainly gold and silver minerals, with particle size accounting for 80.85%; Followed by fine fraction, accounting for12.77%; A small amount of medium and coarse particles. The morphology of gold and silver ores is mainly granular, accounting for 76.6%, followed by breccia and branched gold and silver ores, and a small amount of vein and columnar gold and silver ores. The gold and silver deposits are mainly distributed in the corresponding crystal gap, accounting for 55.32%; Secondly, gold and silver minerals are distributed in the crystal gaps of Yingshi (19. 15%) and galena (8.5 1%). A small amount of silver minerals are produced in the form of other silver minerals, such as Sister and Hexagonal Sister. Tetrahedrite is often embedded with galena in pyrite, and sometimes silver-gold ore, galena and calcite are embedded, accounting for 4.26% in the crystal gap of pyrite.
Mineralization and genesis of the deposit
4. 1 mineralization
According to the relationship between ore-controlling structure and hydrothermal solution and gold mineralization, hydrothermal mineralization period can be divided into four stages: pyrite-isochronous stage, gold-isochronous-pyrite stage, gold-isochronous-polymetallic sulfide stage and isochronous-carbonate stage. The hydrothermal activity of Sizhuang gold deposit is multi-stage and superimposed, which is the result of the staged development of fault structures and the pulsating activity of ore-forming hydrothermal solution. During the hydrothermal activity in the main gold mineralization period, the chemical composition and physical and chemical conditions of the ore liquid are constantly changing, and the crystalline mineral combination is from simple to complex to simple, and the gold content is from less to more and then to less, which shows regular changes.
4.2 Genesis of the deposit
The metallogenic time and space of the deposit are orderly and complete, and the gold mineralization is closely related to the structure. Jiaojiazhu fault is a part of the NNE structural system in this area. It passed through the giant porphyritic medium-grained granodiorite in Shangzhuang unit of guojialing in the early Mesozoic, while the formation age of the giant porphyritic medium-grained granodiorite in Shangzhuang unit of guojialing was the Early Cretaceous (isotopic age 126 ~ 130 Ma). According to the results of isotope determination, the author thinks that the metallogenic age of the deposit is 1 14 ~ 125ma.
The mineralization of Sizhuang gold deposit has experienced a complicated and long evolution process. Ore-forming materials mainly come from surrounding rocks, hydrothermal water sources are mainly atmospheric precipitation and magmatic water, and heat sources are rocks and dikes formed by 1.50 ~ 800 Ma. The genetic type of the deposit belongs to deep melting epithermal gold deposit.
Characteristics of mineralization and enrichment and analysis of prospecting prospect
5. Mineralization and enrichment characteristics of1
5. 1. 1 fault gouge plugging before mineralization is beneficial to mineralization and enrichment.
There is often a layer of fault gouge with different thickness near the ore-controlling fault plane, which has the characteristics of compact structure and poor permeability, and the ore-bearing hydrothermal solution is not easy to escape upward. Therefore, the fractured rock zone (ductile-brittle shear zone) in the footwall of fault mud forms a favorable place for hydrothermal migration and accumulation, and most industrial ore bodies develop in the footwall of main fault.
5. 1.2 Mineralization and enrichment are controlled by tectonic altered rock belts.
The pyrite sericitized fractured rock zone below the main fracture surface of the fault alteration zone is a place with strong tectonic activity, high degree of rock fragmentation, developed fractures and large porosity, which is conducive to the penetration, diffusion and replacement of mineral liquids, extracting more minerals from surrounding rocks and migrating and precipitating with hydrothermal solution to metallogenic structures. Therefore, this part has strong alteration and high mineralization enrichment, and is the main ore body occurrence part of the deposit.
5. 1.3 ore-controlling effect of joint fracture zone
The development of joints and fractures in the footwall of Jiaojia fault zone plays an important role in locating vein-like and veinlet-net vein-like ore bodies. Ore-controlling faults are mostly tensile or torsional, with a tendency consistent with the main structure (sometimes contrary) and a steep dip angle. The Ⅲ vein group of Sizhuang gold deposit occurs in this dense zone of joints and fractures.
5. 1.4 Ore-rich bodies are easy to be formed in the superimposed parts during the metallogenic stage.
The deposit was formed by multi-stage mineralization on the basis of hydrothermal alteration, and the development degree and mineralization intensity of each mineralization stage are different. The first stage (pyrite-isochronous stage) and the fourth stage (isochronous-calcite stage) are poor in gold mineralization, so it is generally impossible to form industrial ore bodies alone. The second and third metallogenic stages (Yingshi-pyrite stage and Yingshi-polymetallic sulfide stage) are characterized by obvious gold mineralization, and industrial ore bodies are easily formed in their overlapping parts.
5.2 Exploration prospect
The exploration and evaluation results of the mining area show that Sizhuang gold deposit in Laizhou is a large-scale low-sulfur gold deposit, which is easy to mine and choose. According to the ore-controlling geological conditions and laws of the deposit, combined with the recent geological research results of Jiaojia metallogenic belt, it is considered that Sizhuang mining area has good prospecting prospects and deep prospecting potential.
1) Ore body I- 1 is one of the main ore bodies of the deposit, which has been closed in the shallow part along the strike and not closed in the deep part along the strike and dip. In the deepest borehole, a thick and stable ore body with a gold grade of 2.62× 10-6 and an engineering ore-controlling elevation of-
2) The Ⅲ ore body group located in pyrite sericitized granite belt is buried deeply (the deepest part is-1003m elevation), with a large number. Due to the limitation of construction conditions and equipment capacity, the engineering control of most ore bodies is insufficient, but the geological characteristics and scale of ore bodies are basically mastered. There is obvious chalcopyrite mineralization in the compound parts of Jiaojiazhu fault and its Sizhuang branch ①, ② and ③ faults. Superimposed with pyrite and lead-zinc ore, many large ore bodies (grade > 5× 10-6, true thickness > 6m) can be seen. Through subsequent geological exploration, the No.3 ore body group still has a good prospecting prospect.
refer to
Jerry Yang, Zhang Xu and Jiang Hongli. 2007. Geological characteristics of Sizhuang gold deposit in Laizhou City, Shandong Province. Shandong land and resources, 23 (5): 6 ~ 10.
(Author Ge Liangsheng)