纳米比亚西北部朝斯组铁矿地质特征研究与初步经济评价

纳米比亚西北部地区朝斯组中赋存大规模铁矿,该铁矿形成于新元古代约730 Ma时期,由于雪球地球的影响,全球在这一时期形成很多大的铁矿。本文通过对朝斯组铁矿岩芯的观察和对岩芯主量元素特征的分析可知朝斯组铁矿主要由Fe_2O_3和SiO_2组成,铁矿中SiO_2含量较高。微量元素特征表明铁矿中富集Co,相对亏损Rb。稀土元素特征表明铁矿中稀土总量均较低,具有相似的REE配分模式,轻稀土相对重稀土亏损,轻微的Eu正异常和明显的Ce负异常。地球化学分析表明铁矿的物质来源兼具陆源沉积物和海相沉积物的特征,Ce的轻微负异常反映了成矿时海水为低氧化环境,而Eu的轻微正异常说明海底低温热液参与了铁矿的成矿过程。朝斯组铁矿石资源量为20亿t,平均品位30%,潜在经济价值为700亿美元。纳米比亚对环境保护严格,采矿的征地成本很高,铁矿所在地区的基础设施非常差,从开采到铁矿运输的成本投入很高,这些都导致纳米比亚铁矿价格优势并不明显。本文认为,如果该地区未来不能发现其他价值更高的共伴生矿产,这些铁矿在目前技术经济条件下开采盈利的前景不明朗。

Geological Characteristics and Preliminary Economic Evaluation of Iron Ore Deposit within the Chuos Formation in Northwest of Namibia

There is a large scale of iron ore deposit within the Chuos Formation in Northwest of Namibia. The iron ore was formed in about 730Ma of Neoproterozoic. Due to the influence of snowball earth, many large iron ores formed in the world during this period. By analyzing the major element of iron ore of Chuos Formation, it consist mainly of Fe2O3T and SiO2, the SiO2 consist is high. Trace element characteristics indicate that Co is enriched in iron ore and Rb is relatively deficient. The characteristics of rare earth elements indicate that the total amount of rare earth elements in iron ore is relatively low, and there is a similar REE distribution model. The light rare earth has relatively heavy rare earth loss, slight positive Eu anomaly and obvious negative Ce anomaly. The source of iron ore is characterized by both terrestrial sources sediments and marine sedimentary deposits. The slight negative anomaly of Ce reflects the low oxidizing environment of seawater during mineralization, but the slight anomaly of Eu indicates that the undersea cryohydrothermal is involved in the deposit of iron ore. The iron ore resources amount to 2 billion tons, average grade 30%, potential economic value is 70 billion US dollars. There is strictly environmental protection law in Namibia, the cost of land acquisition for mining is high, the infrastructure is poor, and the costs for mining and transportation the ore will be high. All these lead to Namibia iron ore price advantage may not be obvious.