陕、甘、川“金三角”地区砂金富集规律及成因类型

THE ENRICHMENT AND GENESIS OF PLACER GOLD IN SHAANXI-GANSU SICHUAN BORDER "GOLD TRIANGLE "REGION

区内砂金矿大都分布在嘉陵江、涪江、白龙江和汉水的河床、河漫滩及Ⅰ级阶地内。在河道由开阔趋向狭窄或由狭窄突变为开阔地段、河流转弯的凸岸(堆积岸)弧形拐弯偏向上游地段、支沟与主河道文汇处靠下游等地段砂金相对富集。砂金主要富集在松散沉积层近底部的含泥砂砾层中。区内砂金矿的成因类型分为冲积型河床砂金矿、冲积型河漫滩砂金矿和冲积型阶地砂金矿三种。成矿时代为全新世早期。形成砂金矿必须具备两个条件:一是必须有砂金矿质来源,即必须有含金地质体的存在;二是有适宜的外营力作用、良好的地貌条件和有利的新构造运动,两者缺一不可。据此划出琵琶寺一河口和刘家坪—椒园里两个找矿远景区。

The studying area lies between 104?00' E to 106?45' E and 32?00' N to 33?40' N. The stratigraphy ranges from Bikou group of pre -Sinian system to Quaternary system,of which Bikou group and Silurian Maoxian group are broadly distributed with bigh Aubackground. Magmatic rocks are developed. Quaternary may be subdivided into 4 units. The placer gold is contained mainly in Holocene alluvium. The neotectonism in this area is typified with inter-mittent raising and vertical viberating,which has made a favourable condition for the forming of Holocene alluvial gold deposits. The distribution of placer gold deposits is in groups. It is closely related to water sys-tems, tectonic positions,magmatic rocks,stratigraphy and geomorphology. The enrichment of placer gold is bound up with the width of river course,the topography of river valley,and the lithology of Au -bearing layer. Three types of genesis of the gold deposits in the area can be recognized: alluvial river placer,alluvial flat placer,and alluvial bench placer. The deposits were formed in early Holocene. Two conditions for the forming of gold deposits are necces-sary:i)the source of gold,i. e. the occurrence of Au-bearing geoloic bodies,and ii)proper ex-ogenetic force, topography and favourable neotectonism. Based on this, Pipasi - Hekou and Liujiaping -Jiaoyuanli potential areas for placer gold exploring are located.