2.2. 1 General situation of regional geology
Kimberlite mining area in southern Liaoning is located at the southern end of Liaodong Tailong, with Yingkou-Kaiyuan NE-trending fault in the west, Yalu River fault in the east and Jinzhou fault in the middle, as shown in Figure 2-5. There are obvious differences in strata and magmatic activities between the east and the west: the east is a new gold uplift, which is in a long-term uplift area, and the ancient metamorphic rocks before Sinian and Yanshan granites are widely exposed; The western part is a set of sedimentary caprocks since Sinian, and only some areas have crystalline basement exposed. The basement lithology is mainly composed of amphibolite, mixed gneiss and schist of Archaean Anshan Group, with the oldest age of 3.2 billion years.
Kimberlite in southern Liaoning is mainly distributed in Fuda depression on the west side of Jinzhou fault. The widely exposed strata are Neoproterozoic Sinian system, which represents a transgression-regression cycle. The lower part of Sinian system is dominated by clastic rocks with flysch formation characteristics; The upper part is mainly carbonate rock with a thickness of about 2000 meters. Cambrian-Ordovician limestone is distributed in Jinzhou and Fuzhou Bay, and Mesozoic Jurassic-Cretaceous limestone is distributed in Dachuan. The strata in this area are gentle, and the whole structure is northeast-southwest monocline structure. Magmatic rocks are not developed, and a small number of rock masses are produced in veins, layers and tubes, with different scales. Besides kimberlite, there are diabase, peridotite, rhyolite and lamprophyre. The ancient basement granite gneiss and Mesozoic Yanshanian granite in the east of Jinzhou fault are exposed in a large area.
See Figure 2-6 for the regional geological map of Wafangdian area.
Figure 2-6 Regional Geological Map of Wafangdian Diamond Mine in Liaoning Province
2.2.2 Regional Strata
(1) Archaean Anshan Group (Arna)
Chengzitan Formation (island arc), the oldest crystalline basement in this area, is distributed in Huaershan and Dawanggou in the east, with a high degree of metamorphism. It consists of a set of amphibole, biotite amphibole, granulite, granulite and magnetite, with a thickness of over 654.38+00000 meters.
(2) Paleoproterozoic
Liaohe Group (Pt 1): scattered in Wafangdian and Qianyuantaizi, not integrated in Anshan Group.
Dashiqiao Formation (Pt 1d): The lithology is mainly dolomitic marble and serpentine marble containing calcium forsterite, with gabbro amphibole and gneiss locally, with a thickness of 8 12 ~ 403m.
Gaixian Formation (Pt 1gx): The lithology is mainly phyllite, schist, slate and biotite granulite, mixed with metamorphic feldspar sandstone and marble lentils, and the thickness is greater than 1827m.
(3) Mesoproterozoic
It is composed of Qingbaikou system and Sinian system, which are widely distributed and are the main surrounding rocks of kimberlite in this area.
Qingbaikou system: including Yongning Formation and Nanfen Formation.
Yongning Formation (Cyh): outcropped in the north of Fuzhou.
Nanfen Formation (Jxn): This area is widely distributed, mainly composed of shale, marl and fine-grained timely sandstone, with a thickness of 690 ~ 13 12m. It is the surrounding rock of Kimberlite No.30, No.34, No.83, 1 10.
1 section (Jxn 1): gray-green, yellow-green shale mixed with purple shale and thin layer of fine-grained timely sandstone.
The second section (Jxn2): light blue thin layer-medium thick marl and purple shale.
Member 3 (Jxn3): grayish yellow thin-medium thick fine sandstone mixed with thin shale.
Sinian: including Qiaotou Formation, Changling Formation, Nanguanling Formation, Ganjingzi Formation, Yingchengzi Formation and Shilitai Formation.
Qiaotou Formation (Qnq): It is widely distributed in this area, and its main lithology is grayish white medium-thick layer of timely sandstone, quartzite mixed with thin layer of timely sandstone and shale (including glauconite), with a thickness of174 ~ 609m. It is the surrounding rock of kimberlite pipelines 50, 5 1, 68 and 74.
Changling Formation (Zc): distributed in Xiaoguanli and Paotai area, silty slate mixed with thin sandstone, with a thickness of1090 ~1145m.
Nanguanling Formation (nZ): It is distributed in the area of Paotai and Xietun, and the lithology is gray-black limestone interbedded limestone with a thickness of 243 ~ 769m.
Ganjingzi Formation (Zg): distributed in Lime Kiln, Lashufang and Koryo City. The main lithology is dolomite limestone with a thickness of 6 13m.
Yingchengzi Formation (Zcy): mainly distributed in Fuzhou Bay area, the main lithology is medium-thick limestone mixed with thin limestone, with a thickness of 622m m..
Shisanlitai Formation (sZ): purple vortex limestone.
(4) Paleozoic
Cambrian (? ): It is mainly distributed in Fuzhou Bay-Lime Kiln area, and the strata are completely exposed, with the alkali plant formation (? 1j), steamed bread group (? 1m), Maozhuang Formation (? 1zm), Xuzhuang Formation (? 2x), Zhangxia Formation (? 2z), Gushan Formation (? 3g), Changshan Formation (? 3c), Fengshan Formation (? 3f) with a total thickness of 789m. The lithology is mainly limestone and shale, in which Maozhuang Formation and Xuzhuang Formation are the surrounding rocks of 1 and No.2 kimberlites. ..
Ordovician (O): distributed in Fuzhou Bay area. The exposed strata are Yeli Formation (O 1y), Liangjiashan Formation (O 1 1) and Majiagou Formation (O 1m). The main lithology is medium-thick crystalline limestone with a thickness of 76m.
Carboniferous (C): The main exposed strata are benxi formation (C 1b) and Taiyuan Formation (C2+3), and the lithology is mainly sandstone and mudstone with coal seams, with a total thickness of more than 273m.
(5) Mesozoic
Jurassic (J): mainly distributed in the fault basin east of Pulandian-Wafangdian. The exposed strata can be divided into Wafangdian Formation (J 1w), Guiyunhua Formation (J3g) and Pulandian Formation (J3p), among which the conglomerate layer at the bottom of Wafangdian Formation (J 1w) contains diamond placer. The total thickness of Jurassic is over 2000 meters.
(6) Cenozoic
Quaternary (Q): It is widely distributed in coastal areas, river valley terraces and plain areas, and its lithology is composed of loess, gravel and clayey silt. Near quaternary diamond placers are distributed in the valley terraces of Toudaogou, Erdaofang and Dashuan diamond mining areas in this area. The thickness of Quaternary system is1~10m.
2.2.3 Regional structure
The structure in this area is complex, mainly fault structure. They are both related and different in formation time, distribution form and performance characteristics, and have different control effects on the occurrence and distribution of kimberlite. The fold structure in this area is undeveloped, and it is generally a northeast monoclinal structure, with gentle stratigraphic occurrence and dip angle of 5 ~ 10. Near the deep fault, there are mainly small east-west anticlines, small synclines and small flexural structures.
(1) regional fault structure
He Fuzhou fault (F 1 fault). It is distributed in the northwest of this area, starting from Changxing Island outside the map sheet in the southwest, and extending to Songshu Town in Santaizi, Dayingzi and Pandatun in the north east, with an overall trend of 50 in the northeast.
Jinzhou fault (F2 fault). The fault starts from Dalian Bay in the south, passes through Jinzhou to Pulandian, Wafangdian and Gaixian in the north, and runs through Liaodong Peninsula. It is the largest deep basement regional fault in this area. Huang thinks it is a lithospheric fault. Jinzhou fault is the boundary of lithofacies construction in this area, and its east and west sides are divided into different geological structural units: Chengzitan fault block in the east and Fuda sag in the west, which control the distribution of Mesoproterozoic, Paleozoic and Mesozoic strata. The fault is also the dividing line of magmatic activity in this area: the east side is dominated by basic intermediate-acid intrusions, and the west side is dominated by the intrusion and ejection of basic super dikes and kimberlites. The fault may have been formed in late Proterozoic. According to aeromagnetic interpretation, the fault belongs to basement fault, which is composed of north-south faults and north-north faults, and is divided into three sections in the region: Jinzhou-Pulandian section in the south; The central part is Pulandian-Wafangdian section; To the north is the northern section of Wafangdian. The south section of Jinzhou fault is dominated by NNE faults; The middle section is dominated by north-south faults, and there are north-northeast faults on both sides of the main fault; The north section is dominated by northeast faults. The local positive magnetic field along Jinzhou fault zone is beaded and banded, which reflects the existence of concealed ultrabasic rocks. Faults are mainly compressive and torsional, with multi-stage activities, and the later activities are not very tensional or tensional.
Figure 2-7 δ z magnetic anomaly map in Wafangdian area
Figure 2-8 Contour map of triangular T-shaped column extending 3 km in Wafangdian area of Liaoning Province
Songmudao-Songshuzhen fault (F3 fault). It is distributed in the central part of this area, starting from Songmu Island in the southwest and reaching Dawanggou, Ganhe, Lidian, Taiyanggou, Erdaogou and other places in the north east, with an overall trend of 35 ~ 45 northeast and an extension of about 40 kilometers. Among them, the Songmudao-Dawanggou fault has obvious characteristics and a large scale, which strikes 30 ~ 40 northeast and tends to 20 ~ 40 southeast. In the fault zone, Nanfen Formation and Qiaotou Formation of Jixian system overthrust the Cambrian system. In the early stage, the NW-trending arc fault and the EW-trending fault were cut in the area of Paotai-Zhuanshan, and the faults met in Laotiangou and Erdaogou, forming No.30 and No.42 lean ore pipes.
Langushan arc fault (F4 fault). It consists of a series of NW-trending folds and faults, which are distributed from Pulandian to the northwest through Sanjiazi, Fort and Koryo Chengzi. The strong compression of fault zone strata led to the repeated occurrence of Jixian and CAMBRIAN strata. The fault was cut by late NE-trending fault.
(2) regional basement structure
In Wafangdian 1: 25000 aeromagnetic survey area, except the basement of Anshan Group is exposed sporadically, most of the rest are covered by Sinian, Quaternary and a small amount of Paleozoic strata.
The Z δ magnetic anomaly map shows that the magnetic field in Wafangdian area is relatively simple, with an east-west positive magnetic field in the middle (Figure 2-7), and the anomaly value is between tens to 100 Nat (nT). Between Majianzi and Laohutun, there is an east-west high-value positive anomaly area with a value above 100 Nat, and its north and south sides are respectively east-west negative magnetic field areas with an amplitude of negative tens of Nats, and the anomaly morphology is relatively regular. There are two low-value negative abnormal areas (the abnormal value is minus several tens of nats) in the Dengtun and Xiaohuangtun areas on the east and west sides of Laoye Temple in the south, and in the areas north of Pandatun and Yangshutun in the north, respectively, and the positive and negative abnormal areas are more obvious on the contour map with δ T polarization extending for 3 kilometers (Figure 2-8).
The sedimentary cover composed of Sinian, Palaeozoic and Quaternary in this area is non-magnetic rock, and the magnetic field variation characteristics in the above areas can only be caused by the fluctuation of the magnetic basement of Anshan Group. It is inferred that the above-mentioned positive magnetic anomaly area should be the uplift part of crystalline basement, and at the maximum value of positive magnetic anomaly, it should be the place with the highest uplift of basement and the thinnest cover. Therefore, the highest basement uplift under the caprock should be in Lvjiatun area and east of Shijiatun. In addition, there is a secondary uplift area west of Zhangjiatun in the west. On the contrary, the deepest basement depression and the thickest caprock are near Dengtun and Xiaohuangtun on the east and west sides of Laoye Temple in the south.
The northern anomaly area is in the north between Pandatun and Yangshutun, and it is also the deepest depression. In the transition zone from the central uplift to the depression centers on the north and south sides, the magnetic field presents a gradient zone with a width of several kilometers, corresponding to the slopes on both sides of the basement uplift. Comparing the T-shaped △ polar anomaly map with the anomaly maps extending 500 meters, 1000 meters and 3000 meters, the north-south boundary between the positive and negative anomaly areas has remained basically unchanged.
The distribution of the above three abnormal zones reflects the main framework of basement uplift and basement fault structure. Generally speaking, there are 10 east-west basement faults under the Great Sinian caprock to the west of Jinzhou fault, which are almost equidistant from north to south. The pre-Sinian crystalline basement of Fuzhou sag is divided into Pandatun-Yangshutun sag in the north, Lujiatun-Shijiatun sag in the middle and Dengtun-Xiaohuangtun sag in the south, and both the north-south sag and the middle sag have secondary uplift and depression. On this basis, the inferred basement structure map of Wafangdian area is compiled, and the gravity profile (A-A 1) running through the north and south of the survey area is inversed. The inferred undulating shape of basement is shown in Figure 2-9, which shows the relationship between the distribution of kimberlite and diamond belt and basement uplift.
Figure 2-9 Gravity Inversion Results of Section A-A
2.2.4 Regional magmatic rocks
Magmatic rocks are well developed in this area, and acidic-ultrabasic rocks are exposed. The lithology is mainly diabase, rhyolite porphyry, granite porphyry, diorite porphyry, basalt, olivine basalt, lamprophyre and kimberlite. Among them, diabase, lamprophyre, olivine basalt and kimberlite occur in veins and bedrock, and the scale is small, showing ne and NE distribution. Basic-ultrabasic rocks are closely related to kimberlite in time and space.
Rhombic porphyry. It is widely distributed in this area, mostly in the form of veins and bedrock, with different widths, generally 0.5 to 20 meters, and the widest point can reach 50 meters. The occurrence changes greatly, the overall strike is 60 ~ 80, and the isotopic age is 95 million ~ 65.438+0.37 billion years, which was formed in the late Mesozoic.
Diorite porphyrite is widely distributed in this area, and its scale changes greatly. Most of them are bedrock and dike-like, and the largest exposed area is 3.5 square kilometers in Taiyanggou.
Diabase is widely exposed, covering almost the whole area, appearing in the form of dikes and bedrock, and its scale changes greatly. The bedrock is mostly distributed in the northwest-northeast direction, with a thickness of 30~50m. The dikes are distributed in the NE direction, and the width is small, which is destructive to kimberlite.
Olive basalt. This kind of rock is closely related to the formation of kimberlite in time and space, and most of them coexist with kimberlite, which is one of the prospecting indicators of kimberlite in this area. The rocks are mainly distributed in veins and some are tubular. The occurrence changes greatly, mainly in the northeast direction. In Maquanzi, the dike passes through the No.9 kimberlite dike, which has played a destructive role.
Lamprophyre. Widely distributed in the region, the strike is mostly NE and NNE. Common ones are Yunhuangyan, amphibolite lamprophyre and olivine lamprophyre. , which formed late and passed through kimberlite dike in this area (Figure 2- 10).
Fig. 2- 10 lamprophyre vein passing through kimberlite