青海老藏沟多金属矿区火山岩岩石化学特征

老藏沟多金属矿区位于秦岭南侧印支褶皱系西段中部,矿床产于上三叠统陆相火山岩系及其火山构造中。所有火山岩均为亚碱性的高铝玄武岩和拉斑玄武岩系列的岩石,这些岩石具有造山带和活动大陆边缘型的钙碱性、钙性火山岩的属性。本区钙碱性、钙性火山岩系是由同源岩浆连续分异形成的产物。对火山岩岩石化学成分研究表明:a.火山岩系具高SiO_2和低TiO_2,Fe_2O_3,Na_2O的特征;b.K_2O/Na_2O比值高(1.70 6.64);c.中酸性火山岩的氧化系数F〔F=FeO/(FeO+Fe_2O_3)〕高,但中性火山岩低。

PETROCHEMISTRY AND GEOLOGIC SIGNIFICANCE OF VOLCANIC ROCKS IN THE LAOZANGGOU POLYMETALLIC AREA QINGHAI PROVINCE

The Laozanggou polymetallic ore ares is situated in the central part of the west section of the Indosinian fold system of the southside of Qinling. The ore deposits occur in the Upper Triassic continental acidic volcanic suite in association with volcanic structures. Allthe volcanic rocks are subalkalic and high-alumium basalts and thaleiitic basslts belonging to calc-alkalic and calcic volcanic series of oro-genic and active continental marginal types. the paper points out that the calc-alkalic and calcic volcanic suites are products of comagmatic continuous differentiation Petrochemistry study shows: 1. these volcanic suites have high SiO_2and low TiO_2, Fe_2O_3, Na_2O; 2. the K_2O/Na_2O ratio is relativelyhigh (1.7-6.64); 3. the oxidation coefficient F(F=FeO/FeO+Fe_2O_2)of the intermediate-acidic volcanic rocks is high, but the F of theintermediate volcanic rocks is low.