柴达木盆地外生硼矿床成矿特征与找矿方向探讨--以雅沙图地区哈克盆地为例

Characteristics and Forming Process of Juhongtu Boron Deposit in Yashatu, Qinghai Province

中国硼矿资源形势不容乐观,急需寻找可替代外生硼矿床。哈克盆地位于柴达木盆地北部边缘,隶属于"溯源找矿"区域,该区硼矿和硼矿化形成为NW-NWW向山前逆冲断裂及NE向断层所控制。对盆地内岩石、沉积物、水系B含量分析结果表明,B含量具明显正异常,水化学组分富B、Li而贫Br、I,∑Ce∑Y比值接近地壳,成矿来源主要为富硼地下水及富硼基岩。针对盆地内典型外生硼矿床——居红土硼矿研究发现如下规律:硼矿体主要分布于晚更新世细粒沉积物之上,反映了稳定条件沉积特征;矿区碎屑沉积物纵向呈明显正粒序变化,硼矿主体自下而上随碎屑粒度由粗变细,B2O3含量由低到高,而自洼地中心向边缘,矿层呈中间厚向两侧变薄并逐渐尖灭的特点;通过光释光测年数据表明,矿床形成于晚更新世≥28 ka;据硅华大部分变为低温石英和C蛋白石以及稀碱金属元素Li>Rb>Cs,表明硅华业经长期"脱水老化"。综合矿区碳酸盐沉积物碳氧同位素和硅钙华底板XRD等研究,将居红土硼矿形成过程划分为3个阶段:I早期硅钙华沉积阶段,II下部硼矿初始沉积阶段,III主体硼矿沉积阶段。

The situation of boron resources is not promising in our country, so it is urgent to find alternative exogenous boron deposits. The Huke basin is located in the northern edge of the Qaidam basin, belonging to a “resource prospecting” area. The NWNWW Piedmont thrust and the NE fault control the formation and the distribution of the boron deposits and the mineralization points in Juhongtu and surrounding areas. The regional rock, the sedimentary and the water content have obvious positive anomalies of B,and the water is rich in B, Li and poor in Br, I, and the ∑Ce/∑Y ratio is close to that of the earth＇s crust, reflecting that the metallogenic source, comes from the groundwater and the boron source rock. From the Juhongtu boron ore and the ＇typical exogenous boron deposit, it is found that the boron ore is distributed in the upper Pleistocene series on fine grained sediments, reflecting stable sedimentary environments： the sediments show a positive change in tire portrait with the granularity of elastic particle size from coarse to line, the change of B2O3 containing grades from low to high and the change of the depression from the center to the edge. The strata thickness is gradually punched out from the middle to the sides. It is the first time to show that the deposit is formed in the late Pleistocene, 28 ka BP： tire silicon is transformed into low temperature quartz and C opal and dilute alkali elements Li 〉 Rb 〉 Cs, which shows that tire sinter has undergone a long-term “dehydration”. Based on the carbonate sediment isotope and XRD analysis, the Juhongtu boron ore forming process is divided into three stages： l-early silicon tufa deposition stage; II- the lower boron ore initial sedimentary stage; and Ill-main boron ore deposition stage. The study of the formation mechanism of boron deposits in Qilian mountain area helps understanding of metallogenic processes.