南秦岭地区花桥富碱辉长岩地球化学特征及其含矿性

Geological and geochemical characteristics and ore-bearing potential of alkali-rich gabbro in Huaqiao,southern Qinling area

南秦岭花桥钛磁铁矿床赋矿岩石为富碱辉长岩,含矿岩相主要为黑云母辉石岩,岩石由含钛普通辉石和黑云母组成。含矿辉长岩体属典型钠质型碱性岩类,Na2O〉K2O,Na2O/K2O值在2.55~5.23之间,碱度率在1.24~1.29之间,MgO含量为5.32%~6.74%,TiO2含量为3.82%~5.84%,Al2O3含量为13.27%~15.06%;属富铁质系列,m/f值为0.37~0.56。在FeO-MgO-Al2O3图解上判别为大陆板内环境。稀土元素总量相对较高,轻稀土元素富集显著,有弱的正Eu异常。花桥钛磁铁矿矿石具有富Fe、Ti、MgO和SiO2不饱和的特点;矿石矿物钛磁铁矿TiO2含量0.415%~23.69%,FeO含量为69.7%~96.18%,Cr2O3含量为0.062%~0.761%。研究表明,南秦岭花桥钛磁铁矿是扬子陆块北缘早古生代幔源低程度部分熔融产物上侵分凝成矿作用的产物。

The ore-bearing rock of the Huaqiao titanomagnetite deposit in southern Qinling area is alkali-rich gabbro,and its ore-bearing petrofacies is mainly biotite-pyroxenolite composed of titaniferous augite and biotite.The ore-bearing gabbro belongs to typical agpaitic alkaline rock,in which Na2O〉K2O,Na2O/K2O is 2.55~5.23,alkalinity ratio（AR） is 1.24~1.29,MgO is 5.32%~6.74%,TiO2 is 3.82%~5.84%,Al2O3 is 13.27%~15.06%,and m/f=0.37~0.56,belonging to ferruginous rock.It occurred in an intraplate environment,as judged by the FeO-MgO-Al2O3 graphical method.The Huaqiao alkali-rich gabbro is also characterized by a relatively high total REE content and a marked enrichment of LREE as well as weak Eu anomaly.The titanomagnetite ores in Huaqiao are enriched in Fe,Ti and MgO,but its SiO2 is unsaturated.In the magnetite,TiO2 is 0.415%~23.69%,FeO is 69.7%~96.18%,and Cr2O3 is 0.062%~0.761%.All these characteristics show that the Huaqiao titanomagnetite deposit resulted from magmatic segregation and mineralization of the low-degree partial fusing product of mantle source material on the northern edge of the Yangtze block in the early Paleozoic period.