Occurrence of supergene nickel ores in the Ha Tri Massive, Hoa An District, Cao Bang Province

Nickel (Ni) laterites are regolith materials derived from ultramafic rocks and play an important role in the world's Ni production. Ni-laterite deposits are the supergene enrichment of Ni formed from the intense chemical and mechanical weathering of ultramafic parental rocks. In Vietnam, the weathering profile containing Ni laterite was first discovered in the Ha Tri massive (Cao Bang). This profile develops on the Ha Tri serpentinized peridotite rocks classified to the Cao Bang mafic-ultramafic complex (North Vietnam) and exhibits thick weathered zone (10 - 15m). This work carried out a detailed study of the weathering profile at the center of Ha Tri massive. Samples from different horizons of the profile were collected and analyzed in detail by XRF, XRD and SEM-EDX methods to establish the relationship between the Ni-rich supergene products and the parental peridotites (lherzolite) rocks in Ha Tri massive. The results show that the saprolite horizon is most Ni-rich in the weathering profile in Ha Tri. In this horizon, Ni-silicate minerals of garnierite group such as pimelite, nepouite and other Mg-Ni silicates have been found. The appearance of minerals of garnierite group is due to the exchange of Mg by Ni during weathering of peridotite minerals, especially olivine, which leads to the enrichment of the supergene Ni. The occurrence of Ni silicates suggests the existence of the supergene Ni ore in the weathering profile of the Ha Tri massive.References Bosio N.J., Hurst J.V., Smith R.L., 1975. Nickelliferousnontronite, a 15 Å garnierite, at Niquelandia, Goias Brazil. Clays Clay Miner., 23, 400-403. Brand N.W., Butt C.R.M., Elias M., 1998. Nickel Laterites: Classification and features. AGSO Journal of Australian Geology Geophysics, 17(4), 81-88. Bricker O.P., Nesbitt H.W. and Gunter W.D., 1973. The stability of talc. American Mineralogist, 58, 64-72. Brindley G.W. and Hang P.T., 1973. The nature of garnierites. Structures, chemical composition and color characteristics. Clay and Clay Minerals, 21, 27-40. Brindley G.W. and Maksimovic Z., 1974. The nature and nomenclature of hydrous nickel-containing silicates. Clay Minerals, 10, 271-277. Brindley G.W. and Wan H.M., 1975. Composition structures and thermal behavior of nickel containing minerals in thelizardite-ne´pouite series. American Mineralogist, 60, 863-871. Brindley G.W., Bish D.L. and Wan H.M., 1979. Compositions, structures and properties of nickel containing minerals in the kerolite-pimelite series. American Mineralogist, 64, 615-625. Cluzel D. and Vigier B., 2008. Syntectonic mobility of supergene nickel ores from New Caledonia (Southwest Pacific). Evidence from faulted regolith and garnierite veins. Resource Geology, 58, 161-170. Colin F., Nahon D., Trescases J.J., Melfi A.J., 1990. Lateritic weathering of pyroxenites at Niquelandia, Goais, Brazil: The supergene behavior ofnickel: Economic Geology, 85, 1010-1023. Das S.K., Sahoo R.K., Muralidhar J., Nayak B.K., 1999. Mineralogy and geochemistry of profilesthrough lateritic nickel deposits at Kansa,Sukinda, Orissa. Joural of Geoogical. SocietyIndia, 53, 649-668. Decarreau A., Colin F., Herbillon A., Manceau A., Nahon D., Paquet H., Trauth-Badaud D.,Trescases J.J., 1987. Domain segregation in NiFe-Mg-Smectites. Clay Minerals, 35, 1-10. Freyssinet P., Butt C.R.M. and Morris R.C., 2005. Oreforming processes related to lateritic weathering. Economic Geology, 100th aniversary volume, 681-722.Garnier J., Quantin C., Martins E.S., Becquer T., 2006. Solid speciation and availability of chromium in ultramafic soils from Niquelandia, Brazil. Journal of Geochemical Exploration, 88, 206-209. Garnier J., Quantin C., Guimarães E., Becquer T., 2008. Can chromite weathering be a source of Cr in soils? Mineralogy Magazine, 72, 49-53. Gleeson S.A., Butt C.R. and Elias M., 2003. Nickel laterites: A review. SEG Newsletter, 54, 11-18. Gleeson S.A., Butt C.R., Wlias M., 2003. Nickellaterites: a review. SEG Newsletter, Society of Economic Geology, 54. Available from www.segweb.org. Golightly J.P., 1981. Nickeliferous laterite deposits. Economic Geology, 75th Anniversary volume, 710-735. Golightly J.P., 2010. Progress in understanding the evolution of nickel laterite. Society of Economic Geology, In Special Publication, 15, 451-485. Manceau A. and Calas G., 1985. Heterogeneous distribution of nickel in hydrous silicates from New Caledonia ore deposits. American Mineralogist, 70, 549-558. Nguyen Van Pho, 2013. Tropic weathering in Vietnam (in Vietnamese). Pubisher Science and Technology, 365p.Ngo Xuan Thanh, Tran Thanh Hai, Nguyen Hoang, Vu Quang Lan, S. Kwon, Tetsumaru Itaya, M. Santosh, 2014. Backarc mafic-ultramafic magmatism in Northeastern Vietnam and its regional tectonic significance. Journal of Asian Earth Sciences, 90, 45-60.Pelletier B., 1983. Localisation du nickel dans les minerais ‘‘garnieritiques’’ de Nouvelle-Caledonie. Sciences Ge´ologique: Me´moires, 73, 173-183.Pelletier B., 1996. Serpentines in nickel silicate ores from New Caledonia. In Grimsey E.J., and Neuss I. (eds): Nickel ’96, Australasian Institute of Miningand Metallurgy, Melbourne, Publication Series 6(9), 197-205. Proenza J.A., Lewis J.F., Galı´ S., Tauler E., Labrador M., Melgarejo J.C., Longo F. and Bloise G., 2008. Garnierite mineralization from Falcondo Ni-laterite deposit (Dominican Republic). Macla, 9, 197-198. Soler J.M., Cama J., Galı´ S., Mele´ndez W., Ramı´rez, A., andEstanga, J., 2008. Composition and dissolution kinetics ofgarnierite from the Loma de Hierro Ni-laterite deposit,Venezuela. Chemical Geology, 249, 191-202. Springer G., 1974. Compositional and structural variations ingarnierites. The Canadian Mineralogist, 12, 381-388. Springer G., 1976. Falcondoite, nickel analogue of sepiolite. The Canadian Mineralogist, 14, 407-409.Svetlitskaya T.V., Tolstykh N.D., Izokh A.E., Phuong Ngo Thi, 2015. PGE geochemical constraints on the origin of the Ni-Cu-PGE sulfide mineralization in the Suoi Cun intrusion, Cao Bang province,  Northeastern Vietnam. Miner Petrol, 109, 161-180.Tran Trong Hoa, Izokh A.E., Polyakov G.V., Borisenko A.S., Tran Tuan Anh, Balykin P.A., Ngo Thi Phuong, Rudnev S.N., Vu Van Van, Bui An Nien, 2008. Permo-Triassic magmatism and metallogeny of Northern Vietnam in relation to the Emeishan plume. Russ. Geol. Geophys., 49, 480-491.Trescases J.J., 1975. L'évolution supergene des roches ultrabasiques en zone tropicale: Formation de gisements nikelifères de Nouvelle Caledonie. Editions ORSTOM, Paris, 259p.Tri T.V., Khuc V. (eds), 2011. Geology and Earth Resources of Vietnam. Publishing House for Science and Technology, 645p (in English). Villanova-de-Benavent C., Proenza J.A., GalíS., Tauler E., Lewis J.F. and Longo F., 2011. Talc- and serpentine-like ‘‘garnierites’’ in the Falcondo Ni-laterite deposit, Dominican Republic. ‘Let’s talk ore deposits’, 11th Biennial Meeting SGA 2011, Antofagasta, Chile, 3p.Wells M.A., 2003. Goronickel laterite deposit. New Caledonia. CRC LEME, p.3

Assessment of heavy metal pollution in abandoned Giap Lai pyrite mine (Phu Tho Province)

Giap Lai pyrite mine had been exploited in the period 1975 - 1999, and abandoned after the mine became closed. This work is conducted with the aim to evaluate the impacts of the abandoned mine to the environment. 23 surface water, 15 ground water and 20 soil samples from the mining area were collected for experiments. Acid production potential and metal leaching of waste materials from tailings were tested. Results show that acid rock drainage (ARD) in the old mining area still occurs, with sulfide-rich tailings and waste rocks being sources of ARD, causing elevated metal concentrations in downstream water bodies. Surface water shows significant pollution of Fe, Mn, Ni and partially As. In the rainy season, the percentage of surface water samples having low pH values as well as metal contents in samples is higher than in the dry season. Metal concentrations in ground water are generally low, but many samples have low pH values, indicating the influence of the ARD. The geo-accumulation index reveals that soil from mining area is moderately contaminated with Ni, Cu, Hg and partially As. Most of the polluted samples are located near old mining pits, waste dumps and tailing ponds. The study also shows that negative effect of Giap Lai pyrite mine on the surrounding water and soil has been ongoing. However, no post-closure remediation measures have been applied at the mine, so there must be appropriate solutions for the acid mine drainage treatment before its being discharged to the environment. Given the facts revealed by this study, it is recommended that the Environmental Protection Law should be fully implemented at mining sites not only during the exploitation but also after their closures.References AMIRA, 2002. ARD Test Handbook. Project P387A Prediction Kinetic Control of Acid  Mine Drainage. AMIRA international May 2002, 42p. Çevik, F., Göksu, M. Z. L.,  Derici, O. B., Fındık,  Ö., 2009. An assessment of metal pollution in surface sediments of Seyhan dam by using enrichment factor, geoaccumulation index and statistical analyses. Environmental Monitoring and Assessment 152, 309-317. EPA, 2000. Abandoned mine site characterization and cleanup hand book, 129p, (https://yosemite.epa.gov/r10/amscch.pdf). Ghrefat, H.A., Abu-Rukah, Y., Rosen, M.A., 2011. Application of  geoaccumulation index and enrichment factor for assessing metal contamination in the sediments of Kafrain Dam, Jordan. Environmental Monitoring and Assessment 178, 95-109. IAEA, 2000. Reference Sheet, reference material. Trace elements in soil. (https://nucleus.iaea.org/rpst/Documents/rs_iaea-soil-7.pdf). INAP, 2009. Global Acid Rock Drainage Guide. International Network for Acid Prevention. (http://www.gardguide.com/index.php/Main_Page). Loska, K., Wiechula, D., Korus, I. 2004. Metal contamination of farming soils affected by industry. Environment International, 30(2), 159-165. MCMPR/MCA, 2010. Strategic Framework for Managing Abandoned Mines in the Minerals Industry, http://www.industry.gov.au/resource/Mining/Documents/StrategicFrameworkforManagingAbandonedMines.pdf. Mhlongo, S.E. and Amponsah-Dacosta, F., 2015. A review of problems and solutions of abandoned mines in South Africa, International Journal of Mining, Reclamation and Environment, DOI: 10.1080/17480930.2015.1044046. Müller, G., 1969. Index of geoaccumulation in sediments of the Rhine River. Geojournal 2, 108-118. Newton, G., et al, 2000. California’s Abandoned Mines. A Report on the Magnitude and Scope of the Issue in the State, Vol.1, 60p. Http://www.conservation.ca.gov/omr/abandoned_mine_lands/AML_Report/Documents/volume1textonly.pdf Nordstrom, D.K., Alpers, C.N., 1999. Geochemistry of acid mine waste. In “Review in Economic Geology, the environmental geochemistry of ore deposits”/Eds. G.S.Plumlee, M.J. Logsdon. Part A: Processes, techniques, and health issues Vol.6A, 133-160. Nowrouzi, M. and Pourkhabbaz, A., 2014. Application of geoaccumulation index and enrichment factor for assessing metal contamination in the sediments of Hara Biosphere Reserve, Iran. Chemical Speciation and Bioavailability,  26(2),99-105. Pham Tich Xuan, Nguyen Van Pho, Hoang Tuyet Nga, Doan Thi Thu Tra, Cai Van Truong, Nguyen Van Thu, Vu Manh Long, 2010. Heavy metal pollution in some metal mines in the Northern Vietnam. Procceding of Conference in commemoration of the 35th day of Establish of VAST. Environment and Energy, Hanoi, 236-244 (in Vietnamese with English abstract). Sobek, A.A., Schuller, W.A., Freeman, J.R. and Smith, R.M., 1978. Field and laboratory methods applicable to overburden and minesoils. Report EPA 600/2-78-054, US Environmental Protection Agency, 204p. Tarras-Wahlberg N.H, Lan T. Nguyen, 2008. Environmental regulatory failure and metal contamination at the Giap Lai pyrite mine, Northern Vietnam. Journal of Environmental Management, 86(4), 712-720. Tran Xuan Toan, 1963. Some characteristics of pyrite mineralization in the Giap Lai deposit, Phu Thọ. Geology 10, 18-24, Hanoi (in Vietnamese). Wei, Z., Wang, D., Zhou, H., Qi, Z., 2011. Assessment of Soil Heavy Metal Pollution with Principal Component Analysis and Geoaccumulation Index. Procedia Environmental Sciences, 10, 1946 -1952. Zawadzki, J and  P. Fabijan´czyk, P., 2013. Geostatistical evaluation of lead and zinc concentration in soils of an old mining area with complex land management. Int. J. Environ. Sci. Technol. 10, 729-742. Ziemkiewicz, P., J. Renton and T. Rymer, 1991. Prediction and Control of Acid Mine Drainage: Effect of Rock Type and Amendment. Proceedings Twelfth Annual West Virginia Surface Mine Drainage Task Force Symposium, April 3-4, Morgantown, West Virginia, Vol.1, 51-54

Environmental isues of mining activities in Tay Nguyen

Intensive mining activities, specially illegal, negatively affect environment in Tay Nguyen. Mining of gold and tin placers, sand and pebble disturbed the landscape, changed river bed caussing river bank erosion. Exploited wastes from mine, for example, kaolin mine in Loc Chau (Lam Dong province) destroyed and retrograded tea land. There observed evidences of acid mine drainage and pollution of heavy metal including Cu, Pb, Hg, et.c in surface water, stream sediments and soils from some gold mines such as Dak Ripen (Kon Tum), Krong A (Dak Lak) and Tra Nang (Lam Dong). Main causes of mining environmental problems are failure of management, so the first and most important measure of mitigation is to improve the management of mining activities.ReferencesBorisenko A.S., Trần Trọng Hòa, V.I. Vasilev, N.K. Morsev, Vũ Văn Vấn, Ngô Thị Phượng, Hoàng Hữu Thành, Trần Tuấn Anh, Phạm Thị Dung, 2008: Phát hiện lần đầu tiên khoáng vật Jonassonite - AuBi5S4 ở Việt Nam. Tạp chí Các Khoa học về Trái Đất, T.30, (3), tr.193-198. Damigos D., 2006: An overview of environmental valuation methods for the mining industry. Journal of Cleaner Production, Volume 14, Issues 3-4, P. 234-247 Dixon-Hardy, D.W. Engels, J.M., 2007: Guidelines and Recommendations for the Safe Operation of Tailings Management Facilities. - Environmental Engineering Science, 24 (5), 14-26. Doolittle, J.J., Frisbee, N.M. and Hossner, L.R., 1992: Evaluation of acid-base accounting techniques used in surface-mine reclamation, Proc. 1992 Meeting of the American Society of Surface Mining and Reclamation, 14-18 June, Duluth, MN, p68-76. Trần Trọng Hòa, Ngô Thi Phượng, Borisenko A.S., Izokh A.E., Vũ Văn Vấn, Bùi Ấn Niên, Trần Tuấn Anh, Phạm Thị Dung, 2005: Đặc điểm địa hóa-đồng vị của quặng hóa vàng Mesozoi sớm và Mesozoi muộn trong mối liên quan với hoạt động magma rìa Đông Nam địa khối Đông Dương. Tạp chí Địa chất, Loạt A, số 295, tr.15-24. Nguyễn Kim Hoàng, Nguyễn Văn Mài, 2010: Đặc điểm khoáng hóa và triển vọng vàng gốc Trà Năng, tỉnh Lâm Đồng. Đại học Quốc gia Tp. HCM. Nilsson J-A, Randhem J., 2008: Environmental Impacts and Health Aspects in the Mining Industry. Department of Energy and Environment. Division of Environmental Systems Analysis. Chambers University of Technology. Göteborg, Sweden, 2008. publications.lib.chalmers.se/records/fulltext/85984.pdf‎ Plumlee, G.S. and Nash, J.T., 1995: Geoenvironmental models of mineral deposits--fundamentals and applications. U.S. Geol. Survey Open-File Report 95-831, p.1-18. Lê Văn Thành, 2004: Khai thác khoáng sản và tác động đến môi trường. Địa chất, N.281 Vũ Văn Vấn, Trần Trọng Hòa, A.S. Borisenko, Ngô Thị Phượng, Trần Tuấn Anh, Trần Hồng Lam, Đặng Trung Thuận, Phạm Thị Dung, 2007: Quặng hóa vàng Tà Năng, đới cấu trúc Đà Lạt: Điều kiện hình thành và bối cảnh địa động lực. Tạp chí Các Khoa học về Trái Đất, T.29, (2), tr.154-160. Báo cáo hiện trạng môi trường tỉnh Lâm Đồng giai đoạn 2006 - 2010: Sở Tài nguyên và Môi trường Lâm Đồng. http://www.lamdong.gov.vn/vi-VN/a/sotnmt/du-lieu-so/moi-truong/Pages/baocaohientrang2006-2010.aspx. Guidebook for Evaluating Mining Project EIAs, 2010: www.elaw.org/files/mining-eia-guidebook/Chapter1.pdf Global Acid Rock Drainage Guide (http://www.gardguide.com/index.php/Main_Page) UNEP, 1997: Industry and environment, mining and sustainable development. http://www.uneptie.org/vol20no4.htmO; 1997.

Study on active tectonic faults using soil radon gas method in Viet Nam

This paper presents the results of soil radon gas measurement in three areas, including Thac Ba and Song Tranh 2 hydropower plants, and the planned locations of the nuclear power plants Ninh Thuan 12 using solid-state nuclear track detectors (SSNTD) with the aim of clarifying the activity of tectonic faults in these areas. The activity of tectonic faults was assessed through radon activity index KRn (the ratio between anomaly and threshold), which was divided into 5 levels as follows ultra-high (KRn 10), high (10≥KRn 5), high (5≥KRn 3), medium (3≥KRn 2) and low (KRn≤2). Soil radon gas measurement results showed that in the radon gas concentrations in the Thac Ba hydropower plant area ranged from 72 Bq/m3 to 273.133 Bq/m3 and maximum radon activity index KRn reached 9.75 (high level). High KRn indexes show Chay River fault active in recent time and the sub-meridian distribution of Rn anomalies suggested a right-slip motion of the fault. Rn concentrations in the Ninh Thuan 12 areas ranged from 6 Bq/m3 to 52.627 Bq/m3, however, the KRn indexes were mostly low (KRn≤3) and the highest value was only 3.42, suggesting that expression of activity of the tectonic faults in this region is not clear, even no expression of fault activity. In the Song Tranh 2 hydropower plant and adjacent areas, radon concentrations ranged from 29 Bq/m3 to 77.729 Bq/m3 and maximum KRn index was 20.16 (ultra-high level). The faults having clearer activity expression are Hung Nhuong - Ta Vy, Song Tra Bong and some high order faults, especially the northwest - southeast segments of these faults or their intersections with the northwest - southeast faults. In addition, the high values KRn in the mentioned intersections can be evidenced for the activeness of northwest - southeast faults at the present time. The studies on active faults using soil radon gas method were performed in areas with very different geological and structural features, but the results are well consistent with the results of previous investigations obtained by other methods. It confirmed the effectiveness and capability of soil radon gas geochemistry applying to study active tectonic faults.ReferencesAl-Hilal M., Al-Ali A., 2010. The role of soil gas radon survey in exploring unknown subsurface faults at Afamia B dam, Syria. Radiat. Meas, 45, 219-224.Amponsah,   P.,   Banoeng-Yakubo,   B.,   Andam,   A., Asiedu, D.,  2008. Soil  radon  concentration along fault systems in parts of south eastern Ghana. J. Afr. Earth Sci. 51, 39-48.Asumadu-Sakyi A.B., Fletcher J.J., Oppon O.C., Qua- shie F.K., Wordson D.A., Adjei C.A., Amartey E.O., Darko E.O. and Amponsah P.,  2011. Preliminary Studies on Geological Fault Location Using Solid State Nuclear Track Detection. Research Journal of Environmental and Earth Sciences, 3(1), 24-31.Baubron, J.-C., Rigo, A., Toutain, J.-P., 2002. Soil gas profiles as a tool to characterize active tectonic are- as: the Jaut Pass example (Pyrenees, France). Earth Planet. Sci. Lett, 196, 69-81.Burton, M., Neri, M., Condarelli, D., 2004. High spatial resolution radon measurements reveal hidden active faults on Mt. Etna. Geophys. Res. Lett, 31, L07618.Ciotoli,  G.,  Etiope,  G.,  Guerra,  M.    Lombardi, S., 1999. The detection of concealed faults in the Ofan- to basin using the correlation between soil gas fracture surveys.   Tectonophysics,  299(3-4), 321-332.Ciotoli, G., Lombardi, S. Annunziatellis, A., 2007. Geostatistical analysis of soil gas data in a high seismic intermontane basin:     Fucino     Plain, central Italy. J. Geophys. Res., 112, B05407, doi:10.1029/2005JB004044.Font, L., Baixeras, C., Moreno, V., Bach, J., 2008. Soil radon levels across the Amer fault. Radiat. 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Radon content of groundwater as an earthquake precursor: evaluation of worldwide data and physical basis. J. Geophys. Res., 86, 9397-9410.Ioannides, K., Papachristodoulou, C., Stamoulis, K., Ka- ramanis, D., Pavlides, S., Chatzipetros, A., Karakala, E., 2003. Soil gas radon: a tool for exploring active fault zones. Appl. Radiat. Isot, 59, 205-213.Israel H. and Bjornsson S., 1967. Radon (Rn-222) and thoron (Rn-220) in soil air over faults. Z. Geophys, 33, 48-64.Kemski, J., Siehl, A., Stegemann, R., Valdivia- Manchego, M., 2001. Mapping the geogenic radon potential in Germany.  Sci.  Total  Environ,  272, 217-230.King  C.Y.,  1978.  Radon emanation on  San  Andreas fault. Nature, 271, 516-519.King, C.Y., King, B.S., Evans, W.C., 1996. Spatial radon anomalies on active faults in California. Appl. Geochem, 11, 497-510.Laskar I., Phukon P., Goswami A.K., Chetry G. and Roy U.C.,   2011.   A possible link between radon anomaly and earthquake. Geochemical Journal, 45, 439-446.Lombardi, S., Voltattorni, N., 2010. Rn, He and CO2 soil gas geochemistry for the study of active and inactive faults. Appl. Geochem, 25, 1206-1220.Moussa M.M., Arabi A-G. M. E., 2003. Soil radon survey for tracing active fault: a case study along Qena- Safaga road, East Desert, Egypt. Radiat. Meas, 37,211-216.Papastefanou C., 2010. Variation of radon flux along active fault zones in association with earthquake occurrence. Radiat. Meas, 45, 943-951.Nguyen Dang Tuc, 2000. Kinematic characteristics of the Red River - Chay River fault zone in Cenozoic.  Journal of  Sciences of the Earth,  22, 174-180 (in Vietnamese).Nguyen Van Pho, Nguyen Trong Yem, 1996. Gas geochemical approach in study of the activity of Red River fault system.  Journal of Geology,  Ha  Noi, series A, 236, 9-10.Nguyen Van Pho, Hoang Tuyet Nga, 1996. Some results of the micro geodynamic maping in Thac Ba area by using of nuclear track detector method. 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Geochemistry of Neogene Basalts in the Nghia Dan district, western Nghe An

Nghia Dan Neogene basalts occur as monogenetic volcanoes and thin lava layers (up to tens of meters thick). They are alkaline basalts and basanites, some containing mantle xenoliths such as spinel lherzolite. Compared with Tay Nguyen (Western Highlands) Cenozoic basalts (for example, Pleiku and DacNong) the Nghia Dan basalts show much lower SiO2 (45-48.5wt.%) and higher FeO*(up to 9-11 wt.%), TiO2 (2.5-3 wt.%) and CaO (9-10 wt.%); they are very high in trace element contents especially Ba, Th, Nb (up to 130 ppm), Sr (up to 2000 ppm) and Eu (up to 4 ppm). Their rare earth concentrations are high, much higher as compared to those of Tay Nguyen. Melting parameter modeling shows the Nghia Dan melts generated from about 3 - 4% partial melting of a combined garnet- spinel- lherzolite source between a pressure range of 20 to 25 Kb (about 75 km deep). The parameters are consistent with the low SiO2 and high trace element, including the rare earth, contents in the Nghia Dan basalts. 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