Study on the geochemistry and subduction-crust mantle interaction of the high potassium-potassium dike rocks in gold deposits concentration zone of east Shandong, China

The paper mainly studied high potassium-potassium dike rocks in gold concen tration zone in Jiaodong of Shandong. The rocks can be divided into three k inds of lithologies, i. e. (I) Lamprophyre, (II) Andesite-porphyrite, (III) Dacite-porphyrite on the basis of factors such as geologic attitude and li thologic character and time-space relationship of gold mineralization etc. These rocks were the products of early mineralization, synchronous and late r mineralization, respectively. Advance on study of geochemistry shows that the geochemical compositions-variations of the major oxides have vague gen eral rules of homologous magmatic fractional-crystallization, and the miner al facies (major component augite and olivine in early stage of transition from lamprophyre to Andesite-porphyrite hornblende and palgioclase by the l ater stage of the transition from andesite-porphyrite to dacite-porphyrite) controlled the magmatic evolution process. The rocks takeof enriched alkal i, high K2O, but lower TiO2, and commonly intensively enriched in LILE (suc h as Ba, Sr, Rb, K, LREE et al.), intensively depleted in coherence element s (such as Cr, Ni et al.), relatively depleted in high fields elements (suc h as Th, Nb, Ti, Y et al.), which proved that magma was derived from thesou rce of enriched mantle. Enriched fugitive constituents and intensively enri ched Ba, Sr and lower Sr/Nd component may be caused by mixing of main subdu ction terrigenous sediment and basaltic ocean crust by dehydration into man tle wedge. The lower partial melting degree (6%similar to 8%) might have be en formed at the special stage from Indo-Chinese epoch on in with an enrich mantle to a depleted mantle at stage of Yanshan, and emplacement environme nt may be the main causes of the different magmatic evolution in the quartz vein-type and altered rock-type of gold deposits.