安徽省泗县山头金刚石砂矿中指示矿物特征研究

Characteristics of Indicator Minerals of the Shantou Diamond Placer Deposit in Sixian County,Anhui Province

安徽省泗县山头地区分布着金刚石砂矿,其金刚石来源一直存在争议,尤其是在安徽省宿州栏杆地区发现了碱性基性岩型的金刚石后,一些学者认为栏杆地区可能是砂矿的来源。本文对山头金刚石砂矿中指示矿物(石榴子石和铬铁矿)进行了电子探针分析,结果显示石榴子石矿物化学式A_(3)^(2+)B_(2)^(3+)(SiO_(4))_(3)中的A主要由Mg^(2+)、Fe^(2+)和Ca^(2+)离子占位,B主要由Al^(3+)离子和少量的Mn^(3+)离子占位,以铁铝榴石(Alm)为主,其次是镁铝榴石(Pyp),属于铁铝-镁铝-钙铝石榴子石系列的G3、G4石榴子石;铬铁矿中Cr_(2)O_(3)的含量绝大多数大于40 wt%,MgO的含量平均在8 wt%左右,TiO_(2)含量在0.11-2.26 wt%之间,属于中铬-铬铁矿,与山东、辽宁金伯利岩中发现的中铬-铬铁矿成分基本一致,说明其物源并非来自栏杆地区碱性基性岩型金刚石原生矿。

The origin of diamonds from the Shantou diamond placer in Sixian County,Anhui Province,has been controversial.After the discovery of alkaline-basic-rock-type diamond in the Lan’gan area of Suzhou,Anhui Province,some scholars believe that the Lan’gan area might be the source of the Shantou diamond placer.The electron microprobe analyses of indicator minerals(garnet and chromite)in Shantou diamond placer show that in the formula A_(3)^(2+)B_(2)^(3+)(SiO_(4))_(3) of garnet,A is mainly occupied by Mg^(2+)、Fe^(2+) and Ca^(2+),while B is mainly occupied by Al^(3+) and a small amount of Mn^(3+),and the garnets are mainly almandine(ALM),fol-lowed by magnesium aluminum garnet(PYP),and belong to G3,G4 garnets of Fe-Al,Mg-Al and Ca-Al gar-net series.The chromites contain more than 40 wt% Cr_(2)O_(3),average 8 wt% MgO,and 0.11-2.26 wt% TiO_(2),and belong to the medium-chromium chromites and are the same as those found in kimberlites of Shandong and Liaoning provinces,which indicates that they did not come from the alkaline-basic-rock-type primary dia-mond deposit in the Lan’gan area.