Genesis of and uranium mineralization in leucogranite, Rossing, Namibia

doi:10.13745/j.esf.sf.2023.5.10

Abstract

Abstract:

The multiphase leucogranite of Rossing can be subdivided into six types, types A-F, but only types D and E form leucogranite uranium deposits. Trace element and Pb isotopic analyses show that the Rossing leucogranite has the characteristics of mixed crustal source, and the two-stage Nd model ages suggest the highly radioactive pre-Damara basement is the source area. The biotite electron probe data show that biotite in type D leucogranite has higher fluorine content compared to types A-C and F, and type D obviously has higher Nb/Ta contents. Types A-C and F leucogranite show a negative correlation between Ba content and Rb/Sr ratio, consistent with muscovite dehydration melting; whilst types D and E show a more complex relationship consistent with biotite dehydration melting. The Rossing area experiences four deformation stages (D1-D4), where the emplacement of types A-C leucogranites occurs no later than D3 while types D and E coincide with D4. The stress transformation during D4 changes the mode of anatexis in the ancient basement from muscovite to biotite melting, and the biotite melt provides fluoride ion, a uranium mineralizer. Therefore, the heterogeneous melting of the ancient basement is the cause of differential uranium enrichment in leucogranite of different phases. The Rossing leucogranite experiences strong crystallization differentiation, where the resulting crystalline minerals are mainly potassium feldspar, biotite, apatite, ilmenite and monazite. The fractional crystallization of biotite may cause uranium depletion, which is unfavorable to the mineralization of residual magma; whereas the fractional crystallization of K-feldspar, ilmenite and monazite is beneficial to the enrichment of uranium and formation of uraninite.

Key words: anatexis, muscovite dehydration melting, biotite dehydration melting, crystal fractionation, Rossing area

CLC Number:

CHEN Xu, FAN Honghai, CHEN Donghuan, CHEN Jinyong, WANG Shengyun. Genesis of and uranium mineralization in leucogranite, Rossing, Namibia[J]. Earth Science Frontiers, 2023, 30(5): 59-73.

Figures/Tables 11

Fig.1 Tectonic setting of the Damara Orogenic Belt (A) and regional distribution of major minerals and metamorphic facies (B). Modified after [3].

Fig.2 Distribution of dome structures, WL fault and uranium deposits in SCZ of the Damara Orogenic Belt. Adapted from [4].

Table 1 Classification of the Rossing leucogranite. Adapted from [8,11].

类型	主要特征	位置	年龄/Ma
A	呈不规则褶皱状,浅灰白色,细-中粒,糖粒状均质结构,以白色长石为主	欢乐谷	547.4±3.6 (LA-ICP-MS U-Pb锆石) ^[11]
B	白色,不等粒结构(细粒至伟晶结构),常见石榴子石、黑云母、电气石	欢乐谷	537.8±4.3 (LA-ICP-MS U-Pb锆石) ^[11]
C	淡红-乳白色,中粒-伟晶结构,含微斜长石和斜长石, 副矿物为磁铁矿、褐铁矿和电气石	欢乐谷	525.4±2.6 (LA-ICP-MS U-Pb锆石) ^[11]
D	呈不规则网状,白色,中-粗粒状结构,原生铀矿化的白岗岩主要由白色长石、烟灰色石英组成,见β硅钙铀矿和磷灰石	欢乐谷	506±8.1(SHRIMP U-Pb锆石)^[25] 497±5.5 (LA-ICP-MS U-Pb锆石) ^[11]
D	呈不规则网状,白色,中-粗粒状结构,原生铀矿化的白岗岩主要由白色长石、烟灰色石英组成,见β硅钙铀矿和磷灰石	湖山	496.1±4.1 (EPMA U-Th-Pb晶质铀矿) ^[26]
E	红-粉红色,颜色及粒度多变,见浅红色长石,有氧化晕圈, 矿物组成与D型相似,或者全部由烟灰色(黑色)石英和粉红色长石构成
F	红色,粗粒-伟晶结构,见粉红色粗粒条纹长石、乳白色石英, 副矿物为磁铁矿和褐铁矿	欢乐谷	511.4±4.3 (LA-ICP-MSU-Pb锆石)^[4]

Fig.3 Harker diagrams for major and U/Th elements of the Rossing leucogranite. Adapted from [8,11].

Fig.4 Chondrite-normalized REE patterns for the Rossing leucogranite (leucogranite data from [11]; normalization values from [28])

Fig.5 Primitive mantle-normalized spider diagrams for the Rossing leucogranite (data see Fig.4)

Fig.6 Plots of elemental ratio vs. TE1,3 for the Rossing leucogranite showing the REE tetrad effect (data from [11,30⇓-32]; base chart from [33])

Fig.7 Triangle diagram for biotite from the Rossing leucoganite showing variation of oxygen fugacity between types A, B, D, F. Modified after [40].

Fig.8 εNd(t)-t diagram for the Rossing leucogranite (modified after [43]). Leucogranite data are from [11]; basement data from [43⇓-45]; uraninite data from [43].

Fig.9 Rb/Sr-Ba diagram for the Rossing leucogranite (data from [11])

Fig.10 Sr-Ba (a, adapted from [60]) and La-(La/Yb)N (b, adapted from [61]) diagrams for the Rossing leucogranite

References 61

[1]	宁福俊, 王杰, 任军平, 等. 纳米比亚达马拉构造带演化和成矿研究综述[J]. 地质调查与研究, 2018, 41(2): 113-120.
[2]	MILLER R M G. Neoproterozoic and early Palaeozoic rocks of the Damara Orogen[M]// The geology of Namibia 2. Windhoek: Ministry of Mines and Energy, Geological Survey, 2008: 1-410.
[3]	GRAY T, KINNAIRD J, LABERGE J, et al. Uraniferous leucogranites in the rössing area, Namibia: new insights from geologic mapping and airborne hyperspectral imagery[J]. Economic Geology, 2021, 116(6): 1409-1434. DOI URL
[4]	陈金勇. 纳米比亚欢乐谷地区白岗岩型铀矿成矿机理研究[D]. 北京: 核工业北京地质研究院, 2014.
[5]	陈金勇, 范洪海, 王生云, 等. 纳米比亚欢乐谷地区白岗岩型铀矿成矿机理剖析[J]. 高校地质学报, 2017, 23(2): 202-212.
[6]	KINNAIRD J A, NEX P A M. A review of geological controls on uranium mineralisation in sheeted leucogranites within the Damara Orogen, Namibia[J]. Applied Earth Science, 2007, 116(2): 68-85. DOI URL
[7]	MCDERMOTT F, HARRIS N B W, HAWKESWORTH C J. Geochemical constraints on crustal anatexis: a case study from the Pan-African Damara granitoids of Namibia[J]. Contributions to Mineralogy and Petrology, 1996, 123(4): 406-423. DOI URL
[8]	NEX P A M, KINNAIRD J A, OLIVER G J H. Petrology, geochemistry and uranium mineralisation of post-collisional magmatism around Goanikontes, southern Central Zone, Damaran Orogen, Namibia[J]. Journal of African Earth Sciences, 2001, 33(3/4): 481-502. DOI URL
[9]	BASSON I J, GREENWAY G. Rössing uranium mine: genesis during late tectonism of the central zone of the Damara Orogen, Namibia[J]. Journal of African Earth Sciences, 2003: 1-15.
[10]	BASSON I J, GREENWAY G. The Rössing uranium deposit: a product of late-kinematic localization of uraniferous granites in the Central Zone of the Damara Orogen, Namibia[J]. Journal of African Earth Sciences, 2004, 38(5): 413-435. DOI URL
[11]	王生云. 纳米比亚欢乐谷地区花岗岩地球化学特征及成因[D]. 北京: 核工业北京地质研究院, 2013.
[12]	吴福元, 刘小驰, 纪伟强, 等. 高分异花岗岩的识别与研究[J]. 中国科学: 地球科学, 2017, 47(7): 745-765.
[13]	CUNEY M. The extreme diversity of uranium deposits[J]. Mineralium Deposita, 2009, 44(1): 3-9. DOI URL
[14]	PORADA H. Pan-African rifting and orogenesis in southern to equatorial Africa and eastern Brazil[J]. Precambrian Research, 1989, 44(2): 103-136. DOI URL
[15]	FOSTER D A, GOSCOMBE B D, NEWSTEAD B, et al. U-Pb age and Lu-Hf isotopic data of detrital zircons from the Neoproterozoic Damara Sequence: implications for Congo and Kalahari before Gondwana[J]. Gondwana Research, 2015, 28(1): 179-190. DOI URL
[16]	MILLER R M G. The Pan-African Damara Orogen of South West Africa/Namibia[M]//MILLER R M. Evolution of the Damara Orogen of South West Africa/Namibia. Johannesburg: Geological Society of South Africa, 1983: 431-515.
[17]	LONGRIDGE L. Tectonothermal evolution of the southwestern Central Zone, Damara Belt, Namibia[D]. Johannesburg: University of the Witwatersrand, 2012: 525.
[18]	MARLOW A. Geology and Rb-Sr geochronology of mineralised and radioactive granites and alaskites, Namibia[M]//MILLER R M. Evolution of the Damara Orogen of South West Africa/Namibia. Johannesburg: Geological Society of South Africa, 1981: 289-515.
[19]	HOFFMANN K H, PRAVE A R. A preliminary note on a revised subdivision and regional correlation of the Otavi Group based on glaciogenic diamictites and associated cap dolostones[J]. Communications - Geological Survey of Namibia, 1996, 11: 77-82
[20]	MILANI L, KINNAIRD J A, LEHMANN J, et al. Role of crustal contribution in the early stage of the Damara Orogen, Namibia: new constraints from combined U-Pb and Lu-Hf isotopes from the Goas Magmatic Complex[J]. Gondwana Research, 2015, 28(3): 961-986. DOI URL
[21]	KUKLA C, KRAMM U, KUKLA P, et al. U-Pb monazite data relating to metamorphism and granite intrusion in the northwestern Khomas Trough, Damara Orogen, central Namibia[J]. Communications - Geological Survey of Namibia, 1991, 7: 49-54.
[22]	MARSH J S. Relationships between transform directions and alkaline igneous rock lineaments in Africa and South America[J]. Earth and Planetary Science Letters, 1973, 18(2): 317-323. DOI URL
[23]	LONGRIDGE L, GIBSON R L, KINNAIRD J A, et al. New constraints on the age and conditions of LPHT metamorphism in the southwestern Central Zone of the Damara Belt, Namibia and implications for tectonic setting[J]. Lithos, 2017, 278/279/280/281: 361-382.
[24]	GOSCOMBE B, GRAY D, HAND M. Variation in metamorphic style along the northern margin of the Damara Orogen, Namibia[J]. Journal of Petrology, 2004, 45(6): 1261-1295. DOI URL
[25]	LONGRIDGE L, GIBSON R L, KINNAIRD J A, et al. Constraining the timing of deformation in the southwestern Central Zone of the Damara Belt, Namibia[J]. Geological Society, London, Special Publications, 2011, 357(1): 107-135. DOI URL
[26]	CROSS A, JAIRETH S, RAPP R, et al. Reconnaissance-style EPMA chemical U-Th-Pb dating of uraninite[J]. Australian Journal of Earth Sciences, 2011, 58(6): 675-683. DOI URL
[27]	BARNES J F H, HAMBLETON-JONES B B. A review of the geologicaland geochemical setting of uraniferous granites in the Damara Orogen[R]. Pelindaba: Nuclear Development Corporation of South Africa, 1978.
[28]	SUN S S, MCDONOUGH W F. Chemical and isotopic systematics of oceanic basalts: implications for mantle composition and processes[J]. Geological Society, London, Special Publications, 1989, 42(1): 313-345. DOI URL
[29]	石强, 徐仲元, 李刚, 等. 原地-半原地深熔花岗岩特征: 以华北克拉通北缘包头地区石榴花岗岩为例[J]. 岩石学报, 2021, 37(1): 211-230.
[30]	JUNG S, HOERNES S, MEZGER K. Geochronology and petrogenesis of Pan-African, syn-tectonic, S-type and post-tectonic A-type granite (Namibia): products of melting of crustal sources, fractional crystallization and wall rock entrainment[J]. Lithos, 2000, 50(4): 259-287. DOI URL
[31]	BAU M. Controls on the fractionation of isovalent trace elements in magmatic and aqueous systems: evidence from Y/Ho, Zr/Hf, and lanthanide tetrad effect[J]. Contributions to Mineralogy and Petrology, 1996, 123(3): 323-333. DOI URL
[32]	BALLOUARD C, POUJOL M, BOULVAIS P, et al. Nb-Ta fractionation in peraluminous granites: a marker of the magmatic-hydrothermal transition[J]. Geology, 2016, 44(3): 231-234. DOI URL
[33]	刘志超, 刘小驰, 俞良军, 等. 喜马拉雅康巴淡色花岗岩的高分异成因及岩浆-热液演化特征[J]. 南京大学学报(自然科学), 2020, 56(6): 800-814.
[34]	RUDNICK R L, GAO S. Composition of the continental crust[M]// Treatise on geochemistry. Amsterdam: Elsevier, 2003: 1-64.
[35]	MONECKE T, KEMPE U, TRINKLER M, et al. Unusual rare earth element fractionation in a tin-bearing magmatic-hydrothermal system[J]. Geology, 2011, 39(4): 295-298. DOI URL
[36]	吕荣平, 金永吉, 顾大钊, 等. 纳米比亚欢乐谷地区铀成矿条件分析及找矿潜力评价[J]. 世界核地质科学, 2015, 32(3): 125-131.
[37]	CORVINO A F, PRETORIUS L E. Uraniferous leucogranites south of Ida Dome, central Damara Belt, Namibia: morphology, distribution and mineralisation[J]. Journal of African Earth Sciences, 2013, 80: 60-73. DOI URL
[38]	黄冉笑, 王果胜, 袁国礼, 等. 伟晶质岩浆的同化混染与分离结晶(AFC)作用及铀成矿效应: 以纳米比亚湖山铀矿为例[J]. 地学前缘, 2022, 29(1): 377-402. DOI
[39]	ABDEL-RAHMAN A F M. Nature of biotites from alkaline, calc-alkaline, and peraluminous magmas[J]. Journal of Petrology, 1994, 35(2): 525-541. DOI URL
[40]	WONES D R, EUGSTER H P. Stability of biotite-experiment theoryand application[J]. The American Mineralogist, 1965, 50(9): 1228-1272.
[41]	MCDONOUGH W F, SUN S S. The composition of the earth[J]. Chemical Geology, 1995, 120(3/4): 223-253. DOI URL
[42]	TAYLOR S, MCLENNAN S. The continental crust: its composition and evolution: an examination of the geochemical record preserved in sedimentary rocks[M]. Oxford: Blackwell Scientific, 1985.
[43]	陈金勇, 范洪海, 王生云, 等. 纳米比亚欢乐谷地区白岗岩型铀矿成矿物质来源分析[J]. 地质学报, 2016, 90(2): 219-230.
[44]	SETH B. Isotope constraints on the origin of Pan-African granitoid rocks in the Kaoko belt, NW Namibia[J]. South African Journal of Geology, 2002, 105(2): 179-192. DOI URL
[45]	FAN H H, CHEN J Y, WANG S Y, et al. Genesis and uranium sources of leucogranite-hosted uranium deposits in the gaudeanmus area, central Damara Belt, Namibia: study of element and Nd isotope geochemistry[J]. Acta Geologica Sinica (English Edition), 2017, 91(6): 2126-2137. DOI URL
[46]	JANOUSEK V, KONOPÁSEKJ, ULRICH S, et al. Geochemical character and petrogenesis of Pan-African Amspoort suite of the Boundary Igneous Complex in the Kaoko Belt (NW Namibia)[J]. Gondwana Research, 2010, 18(4): 688-707. DOI URL
[47]	RIDGE D A M. An investigation into the controls on the distribution of betafite in the SH area, Rossing uranium mine, Namibia [D]St. Andrews: University of St. Andrews, 1993.
[48]	曾令森, 高利娥. 喜马拉雅碰撞造山带新生代地壳深熔作用与淡色花岗岩[J]. 岩石学报, 2017, 33(5): 1420-1444.
[49]	GARDIEN V, THOMPSON A B, GRUJIC D, et al. Experimental melting of biotite+plagioclase+quartz±muscovite assemblages and implications for crustal melting[J]. Journal of Geophysical Research: Solid Earth, 1995, 100(B8): 15581-15591.
[50]	STEVENS G, CLEMENS J D, DROOP G T R. Melt production during granulite-facies anatexis: experimental data from “primitive” metasedimentary protoliths[J]. Contributions to Mineralogy and Petrology, 1997, 128(4): 352-370. DOI URL
[51]	INGER S, HARRIS N. Geochemical constraints on leucogranite magmatism in the Langtang valley, Nepal Himalaya[J]. Journal of Petrology, 1993, 34(2): 345-368. DOI URL
[52]	KNESEL K M, DAVIDSON J P. Insights into collisional magmatism from isotopic fingerprints of melting reactions[J]. Science, 2002, 296(5576): 2206-2208. PMID
[53]	ZENG L, ASIMOW P D, SALEEBY J B. Coupling of anatectic reactions and dissolution of accessory phases and the Sr and Nd isotope systematics of anatectic melts from a metasedimentary source[J]. Geochimica et Cosmochimica Acta, 2005, 69(14): 3671-3682. DOI URL
[54]	ZENG L S, SALEEBY J B, ASIMOW P. Nd isotope disequilibrium during crustal anatexis: a record from the Goat Ranch migmatite complex, southern Sierra Nevada batholith, California[J]. Geology, 2005, 33(1): 53. DOI URL
[55]	ZHANG H, HARRIS N, PARRISH R, et al. Causes and consequences of protracted melting of the mid-crust exposed in the North Himalayan antiform[J]. Earth and Planetary Science Letters, 2004, 228(1/2): 195-212. DOI URL
[56]	ZENG L, GAO L E, DONG C, et al. High-pressure melting of metapelite and the formation of Ca-rich granitic melts in the Namche Barwa Massif, southern Tibet[J]. Gondwana Research, 2012, 21(1): 138-151. DOI URL
[57]	STEPANOV A, MAVROGENES J, MEFFRE S, et al. The key role of mica during igneous concentration of tantalum[J]. Contributions to Mineralogy and Petrology, 2014, 167(6): 1-8.
[58]	PEIFFERT C, NGUYEN-TRUNG C, CUNEY M. Uranium in granitic magmas: part 2. Experimental determination of uranium solubility and fluid-melt partition coefficients in the uranium oxide-haplogranite-H₂O-NaX (X=Cl, F) system at 770 ℃, 2 kbar[J]. Geochimica et Cosmochimica Acta, 1996, 60(9): 1515-1529. DOI URL
[59]	WU F Y, JAHN B M, WILDE S A, et al. Highly fractionated I-type granites in NE China (I): geochronology and petrogenesis[J]. Lithos, 2003, 66(3/4): 241-273. DOI URL
[60]	HANSON G N. The application of trace elements to the petrogenesis of igneous rocks of granitic composition[J]. Earth and Planetary Science Letters, 1978, 38(1): 26-43. DOI URL
[61]	邱检生, 肖娥, 胡建, 等. 福建北东沿海高分异I型花岗岩的成因: 锆石U-Pb年代学、地球化学和Nd-Hf同位素制约[J]. 岩石学报, 2008, 24(11): 2468-2484.