河北承德大庙黑山钒钛磁体矿床地质特征与成因探讨

Geological Characteristics and Genesis of the Heishan V-Ti Magnetite Deposit in Damiao,Chengde Hebei Province

河北承德大庙黑山铁矿床位于大庙斜长岩体南部边缘,红石砬—大庙深断裂附近北侧。矿区内主要岩类为斜长岩,根据蚀变作用可分为钠黝帘石化斜长岩、绿泥石化斜长岩及混染斜长岩等,前者广泛分布于矿区内,后二者常构成铁矿的直接围岩。黑山铁矿苏长岩体与铁矿体有成因联系,主要受近东西向压扭性断层和龙潭沟—岔沟压扭性断裂带构造控制,分布于黑山斜长岩体内。部分苏长岩体中有分异式浸染矿体,在苏长岩接触带及其围岩中的矿体则为贯入式矿体。苏长岩体根据其特征和共生组合,可划分为两个岩石系列:①苏长岩岩石系列(苏长岩类型岩体、含橄苏长岩-苏长岩类型岩体);②二长岩-苏长岩岩石系列(二长岩-苏长岩类型岩体、二长岩-橄榄苏长岩类型岩体)。矿石结构主要为自形—半自形晶粒状结构、格状熔离结构、海绵陨铁结构。矿石构造有致密块状构造、浸染状构造。矿石金属矿物主要为含钒钛磁铁矿(含量3%～60%)、钛铁矿(含量2%～19%)、含钒磁铁矿(含量7%～27%),次有少量含钴黄铁矿、黄铜矿。脉石矿物主要为绿泥石(含量7%～33%),次为斜长石(0%～45%),及其它少量矿物。黑山的矿源苏长岩和中国及世界同类岩石有显著不同,Si、Al、Fe、Ti、P、Na、K含量高,Ca、Mg含量低,这类岩体为形成铁磷矿床提供了物质来源。本区斜长岩、矿源苏长岩铁矿床和铁磷矿床的氧同位素组成δ18O限于一个很窄的变化范围,反映了它们的物质来源和成因类型的同一性。黑山苏长岩、伟晶苏长岩δ34S为+1.3‰～+2.1‰,反映苏长岩浆来源于上地幔。黑山铁磷矿体经铁-钛氧化物矿物对形成温度计计算得出生成温度为615～975℃,显示该岩浆矿床高温成矿特点。研究认为黑山铁矿主要①、②号铁矿体为岩浆贯入成矿。

The Damiao iron deposit is located at the southern margin of the Damiao plagioclase rock body and northern side of the southern edge of Hongshila-Damiao deep fault. Based on the alteration, anorthosite, the major type of rock in the mining area, can be subdivided into saussuritized anorthosite, chloritized anorthosite and mixed anorthosite. The saussuritized one is widely distributed in the mining area, while the others often constitute the surrounding rock of iron mine. Norite body related to the formation of the iron orebody in the Heishan iron mine is controlled by an EW-trending Longtangou-Chagou compressional fault and is distributed mainly within the Heishan anorthosite body. Differential disseminated orebodies occur in partial norite bodies, whereas injection orrebodies occur the contact zone of norite and its surrounding rocks. Based on the characteristics and association of norite, the norite in this region can be divided into two series： （1） norite series （norite-type rock body, olivine-bearing-norite-norite type rock body）; （2） monzonite-norite series （monzonite -norite-type rock body, monzonite-olivine norite rock body）. The ore textures are mainly euhedral-subhedral grain-shaped, grid-shaped dissolution and sponge-shaped siderite textures, with structures being dense massive and disseminated. The ore minerals consist of mainly vanadium-titanium magnetite （3%- 60%）, ilmenite （2%- 19%）, vanadium-bearing magnetite （7%-27%）, and minor cobalt-bearing pyrite and chalcopyrite. Gangue minerals are mainly chlorite （7% -33%）, plagioclase （0% -45%）, and less amount of other minerals. Distinctly different from other norites from both China and world, the Heishan norite is high in Si, A1, Fe, Ti, P, Na, K, and low in Ca, Mg, which provide the source for the iron-phosphate deposit. The oxygen isotope （δ18 O） of anorthosite, norite iron deposits and iron-phosphate deposits in this area are confined within a narrow range, reflecting that they came from the same material source. The δ34S of Heishan norite and pegmatite norite is distributed between ＋ 1.3‰ and ＋2.1 ‰, reflecting the norite magma originated from the upper mantle. The temperature calculation of the apatite in the Heishan iron-phosphate yielded the result of 600-700℃, and the forming temperature of V-Ti magnetite orebody temperature ranges from 700 to -1000℃, showed the characteristics of magma-forming high temperature deposit. This study suggests that the two major iron ore bodies are the products of magma penetration.