关键词: 苏北地区, 辉绿岩床群, 新元古代, 原生金刚石矿, 成矿潜力

Abstract: The northern Jiangsu region, located on the southeastern margin of the North China craton, is a potential target for primary diamond exploration. Although numerous I_b-type diamonds have been discovered in the dolerite of the Langan area, Anhui, no significant breakthrough has been made in diamond exploration in northern Jiangsu. The petrogenesis of these dolerites and their primary diamond mineralization remain poorly understood, which hampers further exploration. This study systematically analyzed the geochemical characteristics of two diamond-bearing and four potentially diamond-bearing dolerite samples from northern Jiangsu, and compared them with the diamond-bearing dolerite from Laozhaishan in the Langgan area. The results show that there are no significant geochemical differences between diamond-bearing and non-diamond-bearing dolerites. Both are tholeiitic sub-alkaline basalts formed in an intraplate setting, enriched in large-ion lithophile elements (e.g., Rb, Ba, La, Eu) and high-field-strength elements (e.g., Nb, U, Nd, Ti). Some diamond-bearing dolerites may have experienced minor crustal contamination, but its effect is limited. The source characteristics indicate a transitional mantle origin, with rare-earth and trace-element patterns intermediate between OIB and E-MORB, suggesting a plume-related origin. The estimated source depth is typically 60-140 km, consistent with the stability depth of I_b-type diamonds, suggesting that the dolerite in northern Jiangsu could serve as a suitable host rock for diamonds. However, the search for primary diamond deposits in dolerite remains challenging. Based on previous research, I_b-type primary diamonds have a relatively short residence time in the mantle. Once they are transported out of the diamond stability field during their early formation, their growth ceases, resulting in limited economic value. Future exploration should therefore more on locating kimberlites or lamproites.

Key words: northern Jiangsu region, dolerite sill swarms, Neoproterozoic, primary diamond deposit, mineralization potential