The applicability of high-precision magnetic survey to find hidden pegmatite-type lithium ore bodies: Taking the Jiajika super−large lithium mine as an example

Objective To address the weak magnetism of pegmatite−type lithium ore bodies, the difficulty in identifying concealed ore bodies at depth, and the limited understanding of the applicability of high−precision ground magnetic surveys to this deposit type, this study investigates the Jiajika super−large lithium deposit in western Sichuan to evaluate the effectiveness and practical conditions of high−precision magnetic surveying for concealed pegmatite−type lithium mineralization.

Methods Based on 1∶50000 high−precision ground magnetic data and four 1∶5000 detailed magnetic profiles, representative rock and ore samples were collected for magnetic susceptibility and remanent magnetization measurements. Reduction to the pole, total horizontal gradient, first vertical derivative, and upward continuation were then integrated to analyze regional and profile−scale magnetic anomalies.

Results Rocks and ores in the Jiajika mining area are generally weakly magnetic, but distinct magnetic differences exist among lithologies and among local samples. Some pegmatites, slates, sandstones, and monzogranites show relatively high magnetic susceptibility and remanent magnetization. The 1∶50000 magnetic data reveal a series of small−scale but relatively strong positive anomalies, together with local negative anomalies, within the Jiajika dome area, which are clearly different from the broad and gentle weak anomalies in the surrounding areas; some of these anomalies correspond well to the distribution of pegmatite veins. The 1∶5000 profile data and upward−continuation results further indicate that the serrated magnetic anomalies in the mining area are not mainly caused by shallow interference, but are closely related to pegmatite intrusion and associated metamorphic alteration zones at depth.

Conclusions Favorable targets in the Jiajika dome can be identified by the combined signatures of local point−like moderate magnetic anomalies and strong horizontal and vertical gradient variations. Although high−precision ground magnetic surveys cannot directly delineate the weakly magnetic pegmatite−type lithium ore bodies themselves, they can effectively trace intrusion−related and metamorphic information associated with mineralization, and therefore provide an important indirect method for locating concealed granitic pegmatite−type lithium ore bodies in western Sichuan and similar rare−metal districts.