盐源盆地重力异常解释推断及成盐远景区预测

doi:10.11720/wtyht.2020.1377

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Abstract

Yanyuan basin is a Cenozoic sedimentary basin in southwest Sichuan basin, where Baishan Formation strata and Yantang Formation strata have rich rock salt. There are four drill holes and a producing well in the salt range of Yanjinggou area, and although the drilling depth of Pu-3 well is 1 001 meters, it does not intersect the salt deposit. The latest 1:50 000 gravimetric data were employed and processed in this paper to build geological-geophysical model of rock-salt minerals by integrating the physical characteristics with gravity anomaly features of rock salt deposit, and a gravimetric profile was simulated by performing the 2.5D forward modelling calculation to infer the geometric and physical parameters of the geological bodies that result in local anomalies. Based on the interpretation of gravity anomalies and the geological understanding of Yanyuan basin, the authors predicted two prospective zones for rock salt exploration in the study area, which has great prospecting significance in Yanyuan basin.

Key words： Yanyuan basin rock salt gravity field salt prospect area

Received: 23 July 2019 Published: 26 October 2020

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	Ting CHEN
	Di YAN
	Zhou YU
	Chen QU
	Zhong-Yu RAN
	Long-Jun QIU

Cite this article:

Ting CHEN,Di YAN,Zhou YU, et al. The interpretation and inference of gravity anomaly and the prediction of salt formation prospect in Yanyuan basin[J]. Geophysical and Geochemical Exploration, 2020, 44(5): 1125-1134.

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https://www.wutanyuhuatan.com/EN/10.11720/wtyht.2020.1377 OR https://www.wutanyuhuatan.com/EN/Y2020/V44/I5/1125

Geological map of the study area
1—Holocene; 2—Pleistocene; 3—Yanyuan group; 4—Lijiang group; 5—combination layer of Zhongwo group and Songgui group; 6—Baitutian group; 7—Baishan group; 8—Yantang group; 9—Qingtianbao group; 10—Xuanwei group; 11—Wujiaping group; 12—Heshan group; 13—Combination layer of Shuhe group and Yangxin group; 14—Emeishan basalt rock; 15—Huanglong group; 16—Combination layer of Posongchong group, Pojiao group, Qujing group, Lanniqing group, Gangou group; 17—Combination layer of longmaxi group and Pizitian group; 18—Triassic gabbro diabase; 19—geological boundaries; 20—unconformity geological boundary; 21—fault of unknown nature; 22—reverse fault; 23—thrust fault; 24—rock salt mine; 25—the research area

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Schematic diagram of salt dome formation in Yanjing river^[9]

Statistical diagram of specimen density

Analysis diagram of salt mine in Yanjing river
1—the Quaternary is not divided into first and second-class terraces, alluvium, diluvium and slope sediments; 2—Quaternary third-stage terrace,alluvium and diluvium; 3—Neogene Xigeda group; 4—Paleogene Hongyazi group; 5—Triassic Yantang group; 6—early Triassic Qingtianbao group; 7—upper Permian Leping group; 8—Himalayan lamprophyre; 9—gabbro diabase; 10—geological boundaries; 11—unconformity boundary; 12—fracture; 13—occurrence; 14—drill hole and serial number; 15—AMT profile and serial number

名称	盐源盐井沟盐矿矿床
概况	东经	101°30'	北纬		27°25'	地理位置	盐源县城南	主矿种	盐矿
区域背景	大地构造位置			盐源—丽江台缘坳陷带
区域背景	区域地球物理			航磁ΔT异常整体呈平静磁场特征,与区内大面积的三叠系沉积物有关,在玄武岩区主要表现为磁高异常特征;重力特征表明该区SN向、EW向梯级带特征最为明显,SN向梯级带特征为金河—箐河断裂及相关次生构造的响应,EW向断裂控制盐源盆地的发育
地质	地层			矿体被第四系、新近系覆盖,围岩为中三叠统盐塘组、白山组
	构造			矿区地表覆盖较厚,三叠系地层出露地段有近EW向断裂
	岩浆岩			煌斑岩、辉绿辉长岩
	赋矿部位			中三叠统白山组中下部,由于塑性流动,盐层侵位逆推的老地层之中
	直接找矿标志			盐溶角砾岩
主要控矿因素				控制盆地发育的EW向断裂边缘形成的坳陷带,是岩盐富集区
空间分布特征	形态			推测为较陡立,厚度大似层状、圆筒状的岩盐层
空间分布特征	埋深			150~1 000 m,孔深1 001 m未穿透岩盐层
矿物组成	矿石类型			盐岩
矿床的地球物理特征及标志	探测目标物			重力低异常区中的中高阻体
	物性特征			密度特征:①矿石密度值为2.185 g/cm³,表现为低密度特征;主要赋矿地层为三叠系白山组、盐塘组。②电性特征:矿石表现为相对高阻、低极化的特征,需要注意的是,在盐矿含水,或在含水构造或地层接触带上盐矿表现为低阻特征。③磁性特征:矿石本身不带磁性,矿体附近的辉绿辉长岩、峨眉山玄武岩等带磁性
	重力异常			重力梯级带富集的重力低异常区,梯级带反映了断裂的存在,断裂附近坳陷带易于盐类矿物沉积,从而形成重力低异常
	MT视电阻率异常			重力梯级带附近,深部显示中高阻异常
	磁异常			无明显磁异常
成矿时代	喜山期
矿床成因	沉积成矿

Geological-geophysical model of salt mine in Yanjing river

Diagram of residual gravity anomaly and the delineation of local gravity anomaly

Comprehensive diagram of geology, bouguer gravity anomaly and residual gravity anomaly in known salt mine
a—geological map;b—bouguer gravity contour map;c—residual gravity contour map

Section fitting result of low gravity anomaly zone (G₂₈)

Comprehensive diagram of geology,bouguer gravity anomaly and residual gravity anomaly in Wadi village
a—geological map;b—bouguer gravity contour map;c—residual gravity contour map

Section fitting result of low gravity anomaly zone (G₃₁)

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