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In northeastern Vietnam, the Khau Loc zone is considered to have high potential for lead-zinc mineralization. The lead isotope data for 18 galena samples and 18 ones of δ34S isotope data (including galena and pyrite samples) were collected from lead-zinc ore deposits in some areas in the Khau Loc zone, including Phia Dam, Khuoi Man, Ban Lin, Lung Dam, and Ta Pan. These were employed to investigate the sulfur and lead isotope geochemical characteristics of Pb-Zn deposits and their significance in this study. The samples were analyzed using the LA-ICP-MS to show that the Pb isotopic ratios of 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb in the galena samples range from 17.8908 to 18.6012, 15.5794 to 16.1025, 38.4420 to 39.2118, with the average values of 18.296, 15.749, and 38.812, respectively. The pyrite and galena samples had the δ34S isotope, ranging from 9.0 to 15.106. The sulfur isotope systematics implies that most of the lead-zinc ore formations originated from marine sedimentary evaporation deposits and magmatic intrusion-volcanic eruption sources rich in silica. The distribution of lead isotopic ratios had a well-defined cluster for each deposit, indicating the formation of lead-zinc deposits and lower crust and orogen trends. In addition, these findings of lead isotopic ratios and δ 34S isotopes proved that the Khau Loc zone is an activated structure with continuous growth in continental crust thickness during the early Proterozoic and Cenozoic periods. Furthermore, the study results also presented the evolution of material sources involved in the formation of lead-zinc ores in the Khau Loc zone.

Major-element geochemistry from two Cores MD05-2899 and MD05-2901 off central Vietnam in the lower continental slope of the western South China Sea is investigated to reconstruct a history of terrigenous sediment variations and East Asian monsoon evolution during the last glacial-interglacial cycle. The results suggest that the Pearl River can play a more important role in contributing terrigenous sediments to the western South China Sea than the Red River in the north, while the Mekong River can transport more terrigenous sediments to the region than the Sunda shelf and the Indonesian islands in the south. The Pearl River provides terrigenous sediments with higher Al2O3, but lower K2O, MgO, and Fe2O3 (Total Fe) than the Mekong River. K2O/Al2O3, MgO/Al2O3, and Fe2O3/Al2O3 ratios are then used as proxies to trace terrigenous sediment variations in the western South China Sea. Higher K2O/Al2O3, MgO/Al2O3, and Fe2O3/Al2O3 ratios indicate strengthened terrigenous sediments input from the southern source and lower the ratios suggest increased terrigenous sediments received from the northern source. These ratios show a glacial-interglacial cycle over the past 130 ka, implying a close relationship with the East Asian monsoon evolution. Northward surface currents forced by strengthened summer monsoon during interglacial periods bring relatively higher amounts of terrigenous sediments from the southern source to the western South China Sea, while relatively higher amounts of terrigenous sediments from the northern source are transported to the western South China Sea by southward surface currents in strengthened winter monsoon during glacial periods. Our study indicates that the terrigenous sediment variations in the western South China Sea are significantly controlled by surface currents under the strong influence of the East Asian monsoon evolution during the last glacial-interglacial cycle.

In Northeast Vietnam, Suoi Thau-Sang Than is considered as a high potential area of polymetallic deposits. 1,720 geochemical samples were used to investigate polymetallic mineralization; thereby polymetallic ore occurrences in this study region were discovered and the statistical and multivariate analysis helps to define geochemical anomalies in some northeastern regions, namely Suoi Thau, Sang Than, and Ban Kep. The statistical method and cluster analysis of geochemical data indicate that the Cu, Pb, and Zn elements are good indicators, and most of them comply with the lognormal or gamma distribution. Based on the third-order threshold, the geochemical anomalies of the content of the Cu, Pb, and Zn elements reflect the concentration of copper forming ore bodies in the mineralized zone, and clearly show the concentration in three distinct zones. The trend surface analysis which was employed to determine spatial variations and relationships among these good indicator elements and anomalous areas revealed relative changes in the content of the indicator elements, and they can be considered as regular. Moreover, the goodness of fit obtained trend functions of Pb and Zn, and Cu elements is a third-degree trend surface model. These results indicate that the models can be useful in studying geochemical anomalies and analyzing the tendency of the concentration of indicator elements in the Suoi Thau-Sang Than region. Additionally, it is suggested that the statistical analysis shows a remarkable potential to use the bottom river sediments in the region to investigate polymetallic mineralization. Moreover, geochemical data can help to evaluate geochemical anomalies of the pathfinder elements and potential mineral mapping of the Suoi Thau-Sang Than region in Northeast Vietnam.

Major-element geochemistry of Miocene sedimentary rock and modern river sediment samples in the Ba River basin, South Central Vietnam are utilized to assess the degree of chemical weathering in the Miocene and the present time. Sediment samples were analysed by X-ray fluorescence (XRF) spectrometer show that Miocene sedimentary rocks contain higher SiO2 and K2O, but lower Fe2O3, TiO2, MgO, Na2O, MnO, CaO, P2O5 than modern river sediment. Major-element geochemistry indicates that Miocene sedimentary rocks and modern river sediment are characterized by stronger depliption of Ca, Na and Mg than K and Si during the chemical weathering in this river basin. The similar relative depleption of Na, Ca, Mg, Si and K between modern river sediments and sedimentary rocks indicate not much deffirent the intensity of chemical weathering in the Miocene and the present time. The chemical index of alteration (CIA) alter from 69 to 93 in Miocene sedimentary rocks (average 74) and from 69 to 78 (average 77) in morden river sediments, indicating moderate chemical weathering in the Ba River basin in the Miocene and the present time.

Clay mineralogy and elemental geochemistry of Core SO18401 on the Vietnam Shelf are used to reconstruct the history of weathering and erosion in central Vietnam over the past 13.2 ka. The variability of the clay species across the 13.2 ka BP together with the age model allows a subdivision into four temporal stages. Provenance analysis based on clay mineralogy indicates that small mountainous rivers in southern-central Vietnam are the major sources of terrigenous sediments on the central Vietnam Shelf. Smectite and kaolinite originated from the chemical weathering of Mesozoic and Neogene-Quaternary basaltic rocks and Paleo-Mesozoic felsic intrusive rocks, respectively, under warm and humid climate conditions; whereas illite and chlorite were mainly derived from physical weathering of Paleo-Mesozoic felsic intrusive rocks and Precambrian metamorphic rocks in central Vietnam. Accordingly, smectite/(illite + chlorite) ratio, together with elemental ratios of Al2O3/K2O, TiO2/Al2O3, and SiO2/Al2O3, can be utilized to reflect the relative importance between chemical weathering and physical weathering/erosion of the parent rocks in southern-central Vietnam. Higher smectite/(illite + chlorite) and Al2O3/K2O ratios indicate a more important role of chemical weathering, and higher TiO2/Al2O3 and SiO2/Al2O3 ratios suggest enhanced contribution of physical weathering and erosion. A combination of these mineralogical and elemental proxies allows the distinction of four stages of weathering and erosion evolution in southern-central Vietnam over the Holocene and Younger Dryas periods. Enhanced physical weathering and erosion took place during the periods ∼13.2–11.0 ka BP (Stage I) and ∼3.9–2.0 ka BP (Stage III), associated with relatively arid conditions. By contrast, strengthened chemical weathering occurred during the periods ∼11.0–3.9 ka BP (Stage II) and 2.0 ka BP to present (Stage IV), corresponding to more warm and humid climatic conditions. Our study suggests that the weathering and erosion history of southern-central Vietnam over the Holocene is mainly controlled by the East Asian monsoon climate.

Nui Phao area (northeastern Vietnam) has a high potential for tungsten resources. The tungsten ore bodies mainly appear in lens-shaped within granitic rocks of the Da Lien complex in the studied area. Minerals accompanying tungsten deposits are composed of fluorite, native gold, native bismuth, chalcopyrite, a lesser amount of allanite, cassiterite, and rare molybdenite. Based on collecting, synthesizing, geological processing data, and the mathematical method, studied objects of the exploration process are quantitatively described. Tungsten oxide (WO3) contents of the major ore body vary from 0.20 to 1.11% with a coefficient of variation (Vc) of 91.2% (unevenly). Generally, the tungsten oxide contents compliance with rules of the standard lognormal distribution. Major tungsten orebody average 56.7 m in thickness and its coefficient of variation (Vm) of 61.2% (unstable). Quantitative calculations reveal the Nui Phao tungsten deposit belongs to the III-type of mining exploration group. To explore this type of minerals, a linear grid pattern should be applied. Results show that the appropriate pattern grid exploration for reserve level 122 is 50 ÷ 60 × 30 ÷ 35 m; these values can be applied to other deposits occurring in similar geological settings.

1,720 chemical, mineral, and petrography samples in the Suoi Thau-Sang Than area, northeastern Vietnam were collected to investigate polymetallic nodules resource. The similarity-analogy in ore geology, direct calculation method for metallization parameters, and mineral resource estimation based on cutoff grade change methods are employed to estimate polymetallic nodules resource from the Suoi Thau, Sang Than, and Ban Kep areas in northeastern Vietnam. The similarity-analogy in ore geology indicates 1,785,000 tons Cu, 12,005,000 tons Pb+Zn, and 195 kg Au in total. The direct calculation method for metallization parameters shows 2,060,000 tons Cu, 13,648,000 tons Pb+Zn, and 224 kg Au in total. These methods display that the Sang Than area contains mainly polymetallic nodules in the studied area. Following the mineral resource estimation based on cutoff grade changes, estimation results indicate potential Pb-Zn nodules resource in the Ban Kep and Cu nodules resource in the Sang Than, while no potential Au nodules resource in the Suoi Thau and the Sang Than as well as the Ban Kep. The estimation results obtained from mineral resource estimation based on cutoff grade changes are suitable with the results from the traditional geometric block methods. Our study suggests that the Sang Than area can be considered as a potential Cu nodules resource, and the Ban Kep area is potential Pb-Zn nodules resource in northeastern Vietnam for future exploitation, while there is no potential polymetallic nodules resource in the Suoi Thau area. Furthermore, the one resource estimation based on cutoff grade changes method displays an overview of the prospect on polymetallic nodules resources, indicating that this method can serve as a basis for the proposed selection of the prospective areas for effective Cu, Pb-Zn, and Au mineral exploration in the Suoi Thau-Sang Than area, northeastern Vietnam.