江西石城海罗岭花岗岩型铌钽矿床岩石地球化学、年代学特征及其地质意义

稀有金属矿产是江西省优势矿产资源,成矿类型以花岗岩型为主,主要分布于赣西和赣北地区,以宜春414超大型钽铌矿为代表,而花岗岩广泛分布的赣南地区鲜有关于燕山期花岗岩型稀有金属矿床的报道。本文以赣南石城海罗岭铌钽矿床为研究重点,结合详细的野外调查,开展花岗岩的岩石学、岩石地球化学和同位素年代学等研究,厘定了海罗岭的中粒斑状黑云母二长花岗岩- 中细粒黑云母二长花岗岩岩石组合,明确了钠长石化叠加白云母化的中粒斑状黑云母二长花岗岩与铌钽矿密切相关的成矿专属性。海罗岭的成矿作用具两阶段特征,早阶段以蚀变花岗岩型钽铌矿为主,赋存于钠长石化白云母化中粒斑状黑云母二长花岗岩中,晚阶段则以花岗伟晶岩型锂矿为主,赋存于云母锂辉石伟晶岩中。海罗岭的花岗岩主要经历了钠长石化、白云母化、黄玉化、绢云母化、硅化等蚀变作用,呈现碱性长石化→云英岩化的演化过程。海罗岭花岗岩具富硅、富碱、富铝,贫钛、镁的特征,其中钠长石化白云母化中粒斑状黑云母二长花岗岩（富钽花岗岩）中F含量为8330×10-6～13076×10-6,平均为10475×10-6,具极低的Nb/Ta值（0. 34~0. 49）、Zr/Hf值（3. 73~4. 19）、稀土总量低（ΣREE为16. 3×10-6~23. 2×10-6）和“四分组”效应等特征,显示其成矿经历了岩浆- 流体相互作用的过程。研究显示,Li矿化富集程度与F含量呈明显的正相关,与稀土总量、K/Rb值呈负相关;Ta矿化富集程度与F含量呈明显的正相关,与Nb/Ta值、Zr/Hf值呈明显的负相关。中细粒黑云母二长花岗岩锆石U- Pb年龄为141. 9±1. 1 Ma,云母锂辉石伟晶岩和碱性长石伟晶岩独居石U- Pb年龄分别为141. 68±0. 69 Ma和137. 62±0. 73 Ma,均归属于早白垩世。研究表明,赣南地区140 Ma左右可能存在一次与钠长石化叠加白云母化中粒斑状黑云母二长花岗岩相关的独特的铌钽矿成矿事件和与花岗伟晶岩相关的锂成矿事件。这一发现打破了以往华南稀有金属主要赋存于燕山期复式岩体晚期二云母花岗岩- 白云母花岗岩中的认识,拓宽了找矿思路,为赣南乃至华南地区稀有金属找矿提供了新的方向。

Petrogeochemical and geochronological characteristics of Hailuoling granite type niobium-tantalum deposit in Shicheng, Jiangxi Province and its geological significance

The granite-type rare metal deposits are Jiangxi Province''s most advantageous mineral resources. These deposits are mainly found in the province''s western and northern regions, with Yichun 414 super-large Ta-Nb deposit serving as a representative. There have been no reports of rare metal deposits associated with the Yanshanian granite type in the widely dispersed granite of southern Jiangxi. We conducted a detailed examination of granite petrology, rock geochemistry, and isotope chronology in our focused study on the Hailuoling Nb-Ta deposit in Shicheng County, southern Jiangxi Province. The rock association in Hailuoling of medium grained porphyritic biotite monzonite granite and medium fine grained biotite monzonite granite has been determined, and the metallogenic specificity of the medium grained porphyritic biotite monzonite granite with albite superimposed muscovite, which is closely related to the niobium tantalite deposit, has been clarified. The mineralization of the Hailuoling Nb-Ta deposit was divided into two stages: the first stage was dominated by altered granite Ta-Nb ore, which was discovered in albitized muscovite medium-grained porphyritic biotite monzogranite, and the second stage was characterized by granite pegmatite type Li ore, which was discovered in mica spodumene pegmatite. The granite from the Hailuoling Nb-Ta deposit experienced a variety of alteration processes, including alkaline feldsparization and mica quartzitization. The granite of the Hailuoling Nb-Ta deposit is rich in silicon, alkali, aluminum, titanium, and magnesium. Furthermore, the albitized muscovite medium-grained porphyritic biotite monzogranite (a tantalum-rich granite) has a fluorine content ranging from 8330× 10^-6 to 13076×10^-6, with a mean of 10475×10^-6. There were very low Nb/Ta and Zr/Hf values, as well as very low whole rare earth concentration. This study found a substantial positive link between the degree of Ta mineralization enrichment and fluorine content, but a significant negative correlation between Nb/Ta and Zr/Hf values. Similarly, enrichment of Li mineralization is correlated with fluorine content but negatively correlated with overall rare earth content and K/Rb value. U-Pb dates of zircon in medium-fine-grained biotite monzogranite were estimated at 141.9±1.1 Ma, while early Cretaceous ages of mica spodumene pegmatite and alkali feldspar pegmatite monazite were 141.68±0.69 Ma and 137.62±0.73 Ma, respectively. This study reveals a distinct Nb-Ta metallogenic event associated with albitization and subsequent muscovitization of medium-grained porphyry biotite monzogranite, as well as a Li metallogenic event associated with granite pegmatite in the southern Jiangxi area about 140 Ma. This discovery broadens the prospecting technique and points in a new avenue for the exploration of rare metals in southern Jiangxi and probably across South China. It calls into question the widely held idea that rare metals in South China are mostly found in the late stages of the Yanshanian granite complex of mica-muscovite granite.