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Abstract Neogene reservoir sand in the Yinggehai-Song Hong (YGH-SHB) and Qiongdongnan basins (QDNB) was derived from the Red River, Hainan Island and the Vietnamese Truong Son Belt. We investigate the sand dispersal pathways through comparisons of detrital zircon geochronology and heavy mineral analyses of modern Vietnamese river sand, Holocene to Recent near-coastal sand from Hainan Island and Vietnam and offshore Neogene sand, and we evaluate the methodologies. Eleven distinct zircon age clusters characterize the Gulf of Tonkin provenances. Red River sand contains the most complex age pattern with ∼35Ma, ∼88Ma, ∼155Ma, ∼250Ma, ∼440Ma peaks and broader pre-Cambrian clusters. The ∼88Ma peak uniquely occurs in Red River sand. Northern Truong Son Belt sand contains ∼35Ma, ∼250Ma, ∼440Ma peaks and pre-Cambrian clusters comparable to the Red River. The lack of Cretaceous zircons and a high proportion of ∼250Ma relative to ∼440Ma zircons distinguishes the northern Truong Son Belt from the Red River. The southern Truong Son Belt is characterized by low proportions of ∼250Ma relative to ∼440Ma zircons and the absence of Cretaceous and Cenozoic zircons. Hainan Island sand is identified by the presence of ∼100 Ma zircons and the absence of Cenozoic and ∼88 Ma zircons. The zircon age patterns suggest simple, although dynamic, sand dispersal pathways with mixed sand sources over much of the basins likely resulting from sediment reworking and down-stream river merging induced by Neogene sea-level fluctuations. Sand in the western YGH-SHB was mainly sourced from the Truong Son Belt, the Red River sourced the northern and central YGH-SHB and QDNB, and Hainan sand was primarily deposited along the island margin. Heavy mineral compositions in the Gulf of Tonkin primarily reflect sediment compositional maturity. Epidote, amphibole, pyroxene and garnet indicate immaturity, whereas a high zircon content tends to indicate high maturity. The use of heavy minerals as provenance indicator should proceed with the utmost caution. Highlights • Truong Son Belt, Red River and Hainan heavy minerals and detrital zircons are analyzed. • Detrital zircons work well as provenance indicators, heavy minerals do not. • Western YGH-SHB sand was mostly derived from the Truong Son Belt. • The central YGH-SHB and QDNB sand has mixed sources dominated by the Red River. • Hainan-derived sand dominate along the Hainan margin. [ABSTRACT FROM AUTHOR]