pilocarpine hydrochloride Primary orebodies occur at to m de

Primary orebodies occur at 150- to >450-m depth, having irregular to elongate lens and vein shapes. Grade control data and exploration drilling define significant concentrations of primary uranium ore around the granite porphyry dikes (Fig. 4; Jiangxi No.264 Geologic Party, 1987). Where they are away from the porphyry dikes, the cryptoexplosive breccia and granite are barren or unmineralized (see cross sections AB and EF in Fig. 4). Ore-hosting rocks underwent widespread hydrothermal alteration. The main identified types of alteration are sericitization, chloritization, carbonatization, red coloration (hematite), and silicification. Like some other uranium deposits (e.g., Huangtian, Aozibei, and Xiaofuzhu) in the Hecaokeng ore field, Caotaobei also record multiple episodes of hydrothermal uranium mineralization that was formed during the mid-Cretaceous (the main stage of primary mineralization, corresponding to the late stage of the Yanshanian Orogeny) and Paleogene (Table 1). Based upon the UPb dating method, the estimated ages of two pitchblende samples from the cryptoexplosive breccia body are 103 and 52 Ma, respectively (Jiangxi No.264 Geologic Party, 1987). It is noted that 103 Ma age of main-stage uranium mineralization coincides with recent geochronologic data that documented a prominent pulse of mid-Cretaceous (ca. 100 Ma) magmatic-hydrothermal activity associated with epithermal CuAuAg and granite-related CuWSnUMo mineralization in Southeast China (Mao et al., 2004, 2008).
Discussion
Conclusions and implication for exploration The Caotaobei uranium deposit of the Hecaokeng ore field was previously considered a typical volcanic-type deposit which resulted from a Yanshanian shoshonitic intermediate volcanism. Allowing for the possibility that Zhang et al. (2001b) have sampled the volcanic breccia containing plastic tuffaceous materials as the cryptoexplosive breccia by mistake, along with the infertility of the intermediate volcanic rocks, the relative age relationships among lavas, granite porphyries, cryptoexplosive breccias, and ores, and the large pilocarpine hydrochloride difference (ca. 30 Ma) between volcanism and main-stage mineralization, it is extremely difficult to defend a volcanogenic hypothesis on the origin of U mineralization at Caotaobei. Based on drill core and grade-control data, rich concentrations of primary uranium ore are common around the granite porphyry dikes, and the cryptoexplosive breccias away from the dikes are barren or unmineralized. Taken together, these observations lead us to believe that the main-stage uranium mineralization is genetically to the granite porphyry intrusions that postdate the shoshonitic volcanic rocks but are broadly coeval with the cryptoexplosive breccias. Zircon overgrowths of mid-Cretaceous age (99.6 ± 5.7 Ma) in the shoshonitic volcanic rock can be attributed to a tectonothermal event associated with the intrusion of the granite porphyries and further supports our genetic reinterpretation. Earlier volcanic event may have just contributed to ground preparation and, to a negligible extent, to the tenor of the ore. Such new explanation is consistent with diamond drill core and grade-control data suggesting the common presence of the rich primary uranium ores around the granite porphyry dikes. The granite porphyry intrusions and associated magma may provide the fluids, ore components, and the thermal energy for U mineralization. However, some other types of fluids and metal sources (e.g., meteoric-derived fluids, which are yet to be identified) could have been substantially involved in the mineralization process. Previous UPb dating results for the main ore indicate mineralization ages of 98 ± 8 Ma and 103 Ma at Xiangshan and Caotaobei, respectively (Jiang et al., 2006 and references therein; Xu, 1984), which are representative of hydrothermal uranium deposits related to (shoshonitic) volcanic rocks in Southeast China. It can thus be suggested that a uranium metallogenic culmination occurred in the mid-Cretaceous (∼100 Ma). During this period voluminous volcanic and intrusive rocks were emplaced in Southeast China under a back-arc extensional regime as a result of northwestward high-angle subduction of the paleo-Pacific plate (Jiang et al., 2011; Zhou et al., 2006; Geng et al., 2006). Similar to Xiangshan in southeastern Jiangxi, the origin of the Caotaobei deposit was also interpreted to be volcanism-related by previous researchers. As a result, intermediate to acid shoshonitic volcanic rocks of mid-Cretaceous age have long been considered important exploration targets for economic uranium mineralization. However, over 30 years of sustained exploration in the Hecaokeng ore field has failed to discover Caotaobei-like mineralization, but resulted in the discovery of over 20 mineral deposits and occurrences which are commonly hosted in the Mesozoic granites, lamprophyres, and breccias. The past exploration successes and failures in the district, coupled with our newly proposed genetic explanation of the Caotaobei deposit and the timing and setting of metallogenesis and magmatism, may point to significant potential for mid-Cretaceous granite-related hydrothermal U deposits in Jiangxi and other parts of Southeast China.