Critical mineral resources of Nb, Ta, Zr, and Hf in China

The two element pairs Nb-Ta and Zr-Hf have similar geochemical behaviors and are critical mineral resources due to their specialized applications in modern high-technology industries. Globally, based on the type of host rock, Nb, Ta, Zr, and Hf resources can be divided into granite- and granitic pegmatite-type, carbonatite-type, alkaline rock-type, and related exogenic deposits. Low reserves and a high import dependency on these metals are important issues for China. There are ca. 50 Nb-Ta deposits in China, with estimated reserves of Nb₂O₅ and Ta₂O₅ of 2.67 × 10⁶ and 0.17 ×10⁶ t, respectively (excluding the Nb reserves in the Bayan-Obo REE-Nb-Fe deposit). Most of these deposits are hosted in aluminous granites, including peraluminous and metaluminous granite types. Examples include the Yichun peraluminous granite-type Nb-Ta deposit in Jiangxi Province, the Guposhan metaluminous granite-type Nb deposit in Hunan and Guangxi and the granitic pegmatite-type Nanping Nb-Ta-Li deposit in Fujian Province. Other minor deposits include the carbonatite-type (e.g., the Miaoya REE-Nb deposit in Hubei Province) and the alkaline rock-type (e.g., the Ba'erzhe REE-Zr-Nb-Be deposit in Inner Mongolia). Niobium-Ta resources in China are located mainly in the western Pacific domain (e.g., the Nanling Range and Jiangnan orogenic belt), the Paleo-Asian Ocean domain (e.g., the Altay Li-Be-Nb-Ta ore belt), the Tethyan domain (e.g., the Songpan-Ganze Li-Be-Nb-Ta and Himalaya Be-Nb-Ta leucogranite ore belts), and at the margins of the Yangtze and North China cratons (e.g., the Nb deposits in the Qinlin orogenic belt). These deposits formed during the Meso-Neoproterozoic (e.g., the Bayan-Obo REE-Nb-Fe deposit during 1.4–1.3 Ga), Paleozoic (ca. 400–380 Ma), early Mesozoic (Paleo-Tethys tectonism; 250–200 Ma), late Mesozoic (the metallogenic explosion in South China; ca. 160–120 Ma), and Cenozoic (Himalaya leucogranite belt; 44–7 Ma). An estimated 500 ´10³ t of ZrO₂ is hosted in both endogenic and exogenic deposits in China. The endogenic Zr-Hf resources are commonly associated with Nb-Ta deposits, due to their similar geochemical behavior. Most of these are hosted in alkaline-peralkaline granites (e.g., the Ba'erzhe REE-Nb-Ta-Zr deposit), along with minor deposits in aluminous granite and granitic pegmatite (e.g., the Koktokay Li-Be-Nb-Ta-Zr-Hf deposit in Xinjiang). There are no occurrences of carbonatite-type Zr-Hf deposits in China. The endogenic Zr-Hf deposits are located primarily along with deep fractures or in rifted regions, including the ore belts of the Tarim and Northern China cratons (e.g., the Boziguo'er alkaline syenite-type deposit in Xinjiang), the western Yangtze Craton (e.g., the Cida alkaline granite-type deposit in Sichuan Province), and the southern Daxing'an mountain range (e.g., the Ba'erzhe alkaline granite-type deposit). These endogenic Zr-Hf deposits formed during the late Paleozoic and Mesozoic. Although endogenic deposits host the main Zr-Hf resources in China, few have been economically exploited due to their low grade and technical challenges. In contrast, domestically available Zr-Hf resources have been exploited from zircon in Quaternary exogenic deposits, including littoral placers (e.g., the Wenchang placers in Hainan Province), fluvial-alluvial placers (e.g., the No. 725 deposit in Guangxi), and weathered crust-type deposits (e.g., the No. 520 deposit in Guangxi). In these exogenic deposits, the ore minerals commonly include zircon, rutile, monazite-(Ce), ilmenite, and other heavy minerals that were derived mainly from Mesozoic granites. Hainan Province is China's largest region of mined exogenic Zr deposits, which occur mostly in Wenchang, Qionghai, Wanning, and Lingshui counties along its southeastern coastline. In summary, although China hosts diverse types of Nb-Ta-Zr-Hf resources and its reserves are large, most of the deposits are of low grade and difficult to utilize. Therefore, future research should focus on ore formation mechanisms, mineral exploration, and improvements in resource recycling, mineral processing, and industrial efficiency.