攀枝花式铁矿赋存岩体顶部普遍发育有富角闪石细脉.本文报道了白马铁矿青杠坪剖面顶部细粒橄榄辉长岩中富角闪石细脉、蚀变带和寄主岩中代表性斜长石、磁铁矿、钛铁矿、角闪石、黑云母和磷灰石等矿物的电子探针分析.岩相学观察表明,细脉中矿物主要为大颗粒角闪石,其间充填钛铁矿、斜长石、方解石;蚀变带中矿物为角闪石、辉石、斜长石、黑云母、磁铁矿及钛铁矿,矿物普遍发生蚀变(如黑云母绿泥石化),斜长石边部也发生溶蚀;靠近蚀变带的寄主岩中矿物主要为斜长石、单斜辉石(二者含量相近),另含少量角闪石、黑云母、磁铁矿和钛铁矿,在钛铁氧化物周围还有黄铁矿、黄铜矿和磷灰石,矿物也发生了轻微的蚀变;而远离细脉的新鲜寄主岩中矿物主要为新鲜的斜长石、单斜辉石(二者含量相近),少量橄榄石、角闪石、黑云母、磁铁矿及钛铁矿.电子探针数据表明,寄主岩中的斜长石An比细脉及蚀变带中的斜长石An要高.新鲜寄主岩中的斜长石主要为拉长石,蚀变带中的斜长石主要为中长石,而细脉中出现了钠长石.运用角闪石全铝压力计对富角闪石细脉中的角闪石颗粒进行了压力和深度的计算,从中心到边部所估算的压力表现出先增大后减小的趋势:69 MPa→121 MPa→167 MPa→128 MPa;运用磁铁矿-钛铁矿共生的温度计和氧逸度计,计算了寄主岩中磁铁矿和钛铁矿平衡时的温度和氧逸度,结果表明,磁铁矿和钛铁矿平衡的温度较低为546～574℃,氧逸度(logfo2)为-20.41～23.83.另外,根据黑云母的Ti-Mg/(Mg+Fe)温度估算图解,靠近蚀变带寄主岩中黑云母的结晶温度为700～720℃.通过讨论分析得出结论:(1)青杠坪镁铁质侵入体侵位后顶部及周围先固结形成顶部细粒橄榄辉长岩带,对底部的含矿流体成矿起到屏蔽层的作用.(2)细脉和蚀变带中斜长石更富Na;由角闪石核部电子探针数据计算出的侵位深度为岩石的真实侵位深度,而由边部电子探针数据计算的深度为流体高压导致的“假”侵位深度;从富角闪石细脉到蚀变带再到寄主岩,矿物的结晶温度逐渐降低,对应流体高温到低温的扩散特点.(3)这种富角闪石细脉可以作为深部矿床的浅部标志,对深部矿床的勘察找靶提供了一种方法.%Amphibole-rich veins are generally developed on the top of Panzhihua-type iron ore host rock.This paper reports the electron microprobe analyses for the representative plagioclase,magnetite,ilmenite,amphibole,biotite and apatite from amphibole-rich veins,alteration zone and fine-grained olivine gabbro on the top of Qinggangping profile,Baima.Petrographic observations show that the minerals formed in veins are coarse grained amphibole with ilmenite,plagioclase and calcite as intersertal fillings.In the alteration zone the minerals are amphibole,plagioclase,biotite,magnetite and ilmenite which are commonly alterated(e.g.biotite chloritized).The plagioclase are corroded on the rim.And in the host rock close to the alteration zone there are major minerals,such as,plagioclase and clinopyxene (similar in contents) and minor minerals,such as,amphibole,biotite,magnetite and ilmenite.There are also apatite and sulfides (pyrite and chalcopyrite)surrounding the titanium oxides.The olivine gabbro away from veins is fresh and major minerals of which are plagioclase and clinopyxene (similar in contents).with small amount of olivine,amphibole,biotite,magnetite and ilmenite.Electron microprobe data show that the An of plagioclase far from the alteration zone is higher than those in the veins and the alteration zone.The plagioclase in fresh host rock are mainly labradorite.The plagioclase in the alteration zone are mainly andesine.And albite occurs in the fine veins.Based on the wholealuminum amphibole geobarometry the pressures recorded by the amphibole from core to rim show a slight drop after increasing,show as:0.69 kbar→1.21 kbar→1.67 kbar and then down to 1.28 kbar.Based on the magnetite-ilmenite equilibrium thermometry and the oxygen fugacity calculation the equillibriun temperature and oxygen fugacity are calculated.The results show that the equilibrium temperature of magnetite and ilmenite is about 546-574 ℃,and the oxygen fugacity (lgfo2) is about-20.41--23.83.According to the biotite Ti Fe/(Mg+Fe) temperature estimation graph,the crystallization temperature of the biotite in the host rock close to alteration zone is between 660 ℃ and 690 ℃.It is concluded that:(1) The top and marginal parts of the Qinggangping mafic intrusion were the first to be solidified forming the fine-grained olivine gabbro which plays the role of shielding layer for fluid mineralization in the depth.(2) The plagioclase in the veins and alteration zone are enriched in Na.The emplacement depth calculated by the electron microprobe on the core of the amphibole gives the true emplacement depth while the others are "false" emplacement depths caused by the fluid pressure.From the amphibole rich veins to alteration zone and then to the host rock,mineral crystallization temperature decreases,corresponding to the fluid diffusion characteristics from higher temperature to the lower.(3)The amphibole rich veins developed in shallow parts can be used as an indicator for deposits in the depth.So,this provides a method for the exploration of deep-seated iron ore-deposits.
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