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白象山铁矿床位于宁芜中生代火山盆地的南段,是南段铁矿田规模最大,最有代表性的一个矿床。矿床广于盆地内走向近南北的小背斜中,是一个产于浅成侵入体与前火山沉积岩接触带上的交代型矿床。与成矿有关的侵入岩是燕山早—中期的闪长岩—辉石闪长岩,受矿区褶皱和断裂控制,成矿母岩体呈南高北低的马鞍形。新鲜岩石为灰绿色,蚀变程度加深则为灰白或深灰绿色,岩石多具似斑状结构和辉绿结构,北部深处为辉长结构。主要矿物斜长石约占70—85%,暗色矿物主要为角闪石,北部含量约15—25%,南部原生暗色矿物少,局部为斜长岩。东部和深部有辉石,原生石英和钾长石极少。斜长石An为29—56,多在33左右,常见密集的环带构造及亮边构造,据文献,亮边长石Ng=1.535,Np=1.526,大致相当于Ab_(75)Or_(25)—Ab_(80)Or_(20)的钾钠长石。角闪石多色性显著,消光角最大的为Ng’(?)C=25°(显微镜下测
The Bai Xiangshan iron ore deposit is located in the south section of the Mesozoic volcanic basin in Ningwu and is the largest and most representative deposit in the southern section of the iron ore field. The deposit is widely distributed in the basin to the small anticline in the north and south, and is a metasomatic deposit on the contact zone between shallow intrusive and volcanic sedimentary rocks. The intrusive rocks associated with metallogenesis are the early-mid-diorite-pyroxene diorites of Yanshanian, which are controlled by fold and fracture in the ore mines. Fresh rock is gray-green, darker alteration is greyish-white or dark gray-green, with many rocks like porphyritic structure and greenery structure, north of the glow-long structure. The main minerals plagioclase account for about 70-85%, the dark mineral is mainly amphibole, the northern content of about 15-25%, the southern native dark mineral less, locally plagioclase. There are pyroxenes in the eastern and deep parts, with very few native quartz and potash feldspar. Plagioclase An is 29-56, which is mostly around 33, and is usually characterized by dense ring structures and bright edges. According to the literature, the bright side feldspar Ng = 1.535, Np = 1.526, which is roughly equivalent to Ab_ (75) Or_ ) -Ab_ (80) Or_ (20) potassium sodium feldspar. Amphibole is highly pleochroic with a maximum extinction angle of Ng ’(?) C = 25 ° (measured under a microscope