Characteristics of Rare Earth Elements in the Deep Carbonate Rocks and Their Geological Significance in the Dachang Tin-polymetallic Deposit of Guangxi

After years of rapid mining, the shallow resources of the polymetallic tin ore bodies in the Bali area, Dachang, have been depleted. Therefore, deep prospecting is imminent. The REEs of limestone samples in the Middle/Upper Devonian from drill holes of ZK39-1 in the Bali area, Dachang, by Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS) have been analysed and the process is presented in this paper. The drilling depth is 1580 m, which is one of the world's deepest hole drilling. The results showed that the amount of the REES (∑REEs) is 3.49-261.07 μg/g with a large range. ∑REEs (3.49-45.81 μg/g) of drill core samples at 1100-1580 m are significantly lower than ∑REEs (188.96-242.36 μg/g) at 1100 m above, which is about 10 times the regional background values and far more than common sedimentary limestone. The ratios of light rare earth elements and heavy rare earth elements (LREEs/HREEs) had a range of 2.96-10.04, which meant that there was a high degree of fractionation between light rare earth elements and heavy rare earth elements. δEu values varied between 0.11 and 1.00 and δCe values ranged from 0.53 to 0.99. The Chondrite-normalized distribution pattern chart was ‘right inclination’ LREE enrichment type. Samples from1100-1580 m had a negative Eu anomaly and Ce had a negative anomaly decreasing from top to bottom. The chondrite-normalized pattern chart of 1100-1580 m drill core samples was similar to that of granite from Dachang, indicating that the carbonates were altered by granite magma and that there might be deep magmatic hydrothermal origin or silicon skarn-type polymetallic mineralization near the granite contact zone, known as the ‘third metallogenic spatial’.