关键词: 拉拉Fe-Cu矿床, 层状侵入体, 成矿系统, 透岩浆流体, 定量化结构分析

Abstract: The layered intrusion has received much attention, however, its petrogenensis and metallogenic model are still debatable. Here, we report for the first time the mafic ore-bearing layered intrusions in the Lala Fe-Cu ore district. This discovery will aid metallogenic research on the Fe-Cu ore, Lala district for a better understanding of the intrusion and metallogenic processes of layered intrusion. Field observation showed that the layered intrusion was composed of nine lithofacies zones, with intrusive contacts between adjacent zones and mirror imaging between the upper and lower halves of the facies. Microscopic observations, X-ray diffraction and CDC analyses of the upper five lithofacies zones indicated that the mineral composition and structural parameters of the adjacent facies zones were markedly different, which may suggest that the intrusion was formed by 45 pulsed invasions. Each lithofacies zone has the porphyritic texture. Phenocrysts in the 1st4th facies zones were mainly hornblende, mica and Ti-Fe oxide, while muscovite, potash feldspar and quartz mainly in the 5th , and big clinopyroxene and calcite phenocrysts made up the 3rd and 4th facies zones, respectively. The hydrous mineral in phenocryst implied that all ore-forming magmas contained saturated or supersaturated H2O + CO2 volatiles, but had different origin for each facies zone. Based on the phenocryst mineral assemblage, quantitative structural parameters and parameter variation trend, one can speculate that 35  magma chambers of different depths existed under the Lala sill. These magma chambers were packed with evolved magmas of varied compositions, possibly enriching the corresponding ore-forming metals. As the deep metallogenetic fluid entered this magmatic system, ensuing domino effect might lead to mass release of all kinds of metallogenetic fluids. The Lala-type sill might act as shield for the ore-forming materials to aggregate at a large scale and form super-size deposits. It is worth noting that the rich ore lithofacies zone experienced the latest emplacement, similar to that of the Panzhihua-type iron deposit. Therefore, the petro-metallogenetic model of the Lala sill may be applicable to the Panzhihua-type iron deposit.

Key words: Lala Fe-Cu deposit, layered intrusion, mineral system, transmagmatic fluid, crystal size distribution