成矿碳酸岩的实验岩石学研究现状与展望

doi:10.13745/j.esf.sf.2021.8.3

摘要/Abstract

摘要：

火成碳酸岩及其风化产物是全球战略性关键金属稀土元素(REE)和铌(Nb)的主要来源。因此,对关键金属在火成碳酸岩中的超常富集机理研究具有重要的科学意义。研究表明成矿碳酸岩常常与碱性杂岩体存在密切的时空联系,因而母岩浆应属于碳酸盐化的硅酸盐岩浆,并以霞石岩岩浆为主。针对碳酸岩关键金属矿床的成岩成矿过程,已有实验发现母岩浆在地壳内的演化过程中,既可以通过分离结晶作用,也可以通过液态不混溶作用形成碳酸岩。然而,更加接近自然样品的多组分体系的实验均表明液态不混溶作用总是先于碳酸盐矿物分离结晶作用。因此,液态不混溶作用对关键金属成矿过程有着不可忽视的作用。尽管如此,已有不混溶实验表明当碳酸盐熔体和硅酸盐熔体发生不混溶之后,关键金属REE与Nb总是优先分配到硅酸盐熔体(碱性岩)中,但是在成矿杂岩体中,REE与Nb是高度富集在碳酸岩中。虽然不混溶实验表明REE与Nb在碳酸盐-硅酸盐熔体中的分配系数与含水量有关,即与熔体的聚合程度有关,但是绝大部分成矿碳酸岩成矿过程一般并不富水,所以碳酸岩中REE和Nb等关键金属元素超常富集的机理并不明确。因此未来的研究应重点关注在碳酸岩演化的过程中,除了水以外,其他配体对于关键金属元素在不混溶硅酸盐-碳酸盐熔体之间分配系数是否有影响,从而找到控制碳酸岩中关键金属成矿的关键。

关键词: 碳酸岩, 关键金属, 液态不混溶, 实验岩石学, 分配系数

Abstract:

Carbonatites and their surface weathering products constitute the main source of strategic metals, such as REE and Nb. Thus it is of great scientific significance to understand the extraordinary enrichment mechanism of strategic elements in carbonatites. Previous studies show that the mineralized carbonatites are closely associated with alkaline complex, indicating the parent magma is carbonated silicate magma which is dominated by carbonated nephelinite. Some experiments showed that both immiscibility and fractional crystallization could lead to carbonatite formation during the crustal evolution of parent magma. However, multicomponent experiments have clearly shown that liquid immiscibility always occurs prior to fractional crystallization of carbonate minerals, and thus immiscible separation of carbonatite from silicate melts plays an important role in the mineralization of strategic metals in carbonatites. However, in contrast to the fact that REE and Nb are naturally hosted in carbonatite, the immiscibility experiments showed that the strategic metals (REE and Nb) are preferentially partitioned into the silicate melt (alkaline silicate rocks). Although the partition coefficients of REE and Nb in carbonate-silicate melt is dependent on the water content, i.e., the degree of polymerization of the melt, the mechanism by which strategic metal elements (REE and Nb) are extremely enriched in carbonatites is enigmatic as the formation of mineralized carbonatites is mostly under anhydrous condition. Therefore, in order to elucidate the key controlling factors for the mineralization of critical metals in carbonatite, further studies should focus on whether other ligands, in addition to water, may influence the partition coefficient of critical metals between the immiscible carbonatitic and nephelinitic melts.

Key words: carbonatite, critical metals, liquid immiscibility, experimental petrology, partitioning coefficient

中图分类号:

P589
P588.15

杨道明, 潘荣昊, 王萌, 侯通. 成矿碳酸岩的实验岩石学研究现状与展望[J]. 地学前缘, 2022, 29(1): 54-64.

YANG Daoming, PAN Ronghao, WANG Meng, HOU Tong. Current research progress and emerging trends in experimental study of mineralized carbonatite[J]. Earth Science Frontiers, 2022, 29(1): 54-64.

图/表 8

图1 500 MPa下CO2和H2O在镁铁质熔体中的溶解度(a)及100 MPa和500 MPa下CO2和H2O在富碱镁铁质熔体中的溶解度(b)(据文献[28]修改)

Fig.1 Correlation of H2O and CO2 solubilities in mafic melts at 500 MPa (a) or in alkali-rich mafic melts at 100 and 500 MPa (b). Modified after [28].

图2 CaO-MgO-SiO2-CO2体系中,2.5 GPa下CO2饱和时液相面部分示意图(a)和CaCO3-(Na, K)2CO3伪二元系相图(b) (a据文献[38]修改;b据文献[29]修改) a—Qz为石英,Opx为斜方辉石,Cpx为单斜辉石,Fo为镁橄榄石,Cd为白云石固溶体,Ccd为碳酸盐固相,Cm为菱镁石固溶体,灰色虚线为两个液相面的交线,2L为两相不混溶的液相线;b—灰线为实验合成体系,黑线为天然的Oldoinyo Lengai体系,灰色虚线为根据实验推测出的液相线,L为液相,ss为固溶体,cc为方解石,nyer (nyerereite)为尼碳钠钙石,nc为碳酸钠。

Fig.2 (a) Schematic CO2-saturated liquid phase diagram (partial) for CaO-MgO-SiO2-CO2 system at 2.5 GPa (modified after [38]) and (b) phase diagram of CaCO3-(Na,K)2CO3 pseudobinary system (modified after [29])

图3 SNAC+CO2体系中,不混溶相图 (据文献[43]修改)

Fig.3 Phase diagram showing immiscibility field in SNAC+CO2 system. Modified after [43].

图4 含挥发分(H2O/F/Cl)霞石岩+10%方解石体系相平衡关系图(a)和(Na2O+K2O)-(SiO2+TiO2+Al2O3)-(CaO+MgO+FeO)体系的三元相图(b) (据文献[12]修改)

Fig.4 (a) Phase equilibria of nephelinite and calcite (10%) with presence of volatiles (H2O/F/Cl) and (b) immiscibility field in (Na2O+K2O)-(SiO2+TiO2+Al2O3)-(CaO+MgO+FeO) ternary system. Modified after [12].

表1 碳酸盐化碱性岩浆液态不混溶实验条件

Table 1 Experimental conditions forthe carbonated alkaline magmatic liquid immiscibility experiments

实验	压力p	温度T/℃	氧逸度	初始物质H₂O 含量/%
Veksler等^[17]	100 MPa	800~950	NNO	0~11.3
Martin等^[46]	1~3 GPa	1 150~1 260	FMQ-FMQ+4	0~3.9
Nabyl等^[48]	0.4~1.5 GPa	725~975	FMQ-FMQ+2	0.77~12

图5 在无水系统与含水系统中,微量元素在碳酸盐与硅酸盐熔体中的分配系数 (数据引自文献[17,46,48])

Fig.5 Partition coefficients for trace elements in water-bearing or anhydrous carbonate-silicate melts. Data from [17, 46, 48].

图6 初始物质的水含量、温度、压力及氧逸度与碳酸盐熔体-硅酸盐熔体分配系数图解 (数据引自文献[17,46,48]) CL—碳酸盐熔体;SL—硅酸盐熔体;D—元素分配系数。

Fig.6 Plots of Nb (left panel) and REE (right panel) partition coefficients in carbonatite-silicate melt vs. water content (a, b), pressure (c, d), temperature (e, f) and oxygen fugacity (g, h) of the starting materials. Data from [17,46,48].

图7 熔体聚合程度对分配系数的影响(a)及硅酸盐熔体与磷酸盐、硫酸盐、氟化物和氯化物的熔盐之间的分配系数曲线(b) (据文献[17,46])

Fig.7 Effect of melt polymerization on REE partition coefficients (a) and REE partition coefficients in silicate melts containing immiscible phosphate, sulfate, fluoride and chloride molten salts (b). Data are adapted from [17,46].

参考文献 64

[1]	LE MAITRE R W. Igneous rocks: a classification and glossary of terms[M]. Cambridge: Cambridge University Press, 2002: 236.
[2]	FOLEY S F, YAXLEY G M, ROSENTHAL A, et al. The composition of near-solidus melts of peridotite in the presence of CO₂ and H₂O between 40 and 60 kbar[J]. Lithos, 2009, 112(Suppl 1):274-283. DOI URL
[3]	HAMMOUDA T, MOINE B N, DEVIDAL J L, et al. Trace element partitioning during partial melting of carbonated eclogites[J]. Physics of the Earth and Planetary Interiors, 2009, 174(1/2/3/4):60-69. DOI URL
[4]	DASGUPTA R, HIRSCHMANN M M. The deep carbon cycle and melting in Earth’s interior[J]. Earth and Planetary Science Letters, 2010, 298(1/2):1-13. DOI URL
[5]	DASGUPTA R, HIRSCHMANN M M, WITHERS A C. Deep global cycling of carbon constrained by the solidus of anhydrous, carbonated eclogite under upper mantle conditions[J]. Earth and Planetary Science Letters, 2004, 227(1/2):73-85. DOI URL
[6]	KISEEVA E S, LITASOV K D, YAXLEY G M, et al. Melting and phase relations of carbonated eclogite at 9-21 GPa and the petrogenesis of alkali-rich melts in the deep mantle[J]. Journal of Petrology, 2013, 54(8):1555-1583. DOI URL
[7]	王凯怡, 杨奎峰, 范宏瑞, 等. 白云鄂博矿床研究若干问题的探讨[J]. 地质学报, 2012, 86(5):687-699.
[8]	陈唯. 碳酸岩型铌矿床成矿作用[J]. 矿物学报, 2015, 35(增刊):276.
[9]	陈唯. 碳酸岩中高普通铅副矿物原位微区U-Th-Pb测年[J]. 矿物学报, 2015, 35(增刊):694.
[10]	WOOLLEY A R, CHURCH A A. Extrusive carbonatites: a brief review[J]. Lithos, 2005, 85(1/2/3/4):1-14. DOI URL
[11]	BAILEY D K, KEARNS S. New forms of abundant carbonatite-silicate volcanism: recognition criteria and further target locations[J]. Mineralogical Magazine, 2012, 76(2):271-284. DOI URL
[12]	KJARSGAARD B A. Phase relations of a carbonated high-CaO nephelinite at 0.2 and 0.5 GPa[J]. Journal of Petrology, 1998, 39(11/12):2061-2075. DOI URL
[13]	CHAZOT G, MERGOIL-DANIEL J. Co-eruption of carbonate and silicate magmas during volcanism in the Limagne graben (French Massif Central)[J]. Lithos, 2012, 154:130-146. DOI URL
[14]	谢玉玲, 曲云伟, 杨占峰, 等. 白云鄂博铁、铌、稀土矿床: 研究进展、存在问题和新认识[J]. 矿床地质, 2019, 38(5):983-1003.
[15]	SMITH M P, MOORE K, KAVECSÁNSZKI D, et al. From mantle to critical zone: a review of large and giant sized deposits of the rare earth elements[J]. Geoscience Frontiers, 2016, 7(3):315-334. DOI URL
[16]	WOOLEY A R, KJARSGAARD B A. Carbonatite occurrences of the world: map and database[J]. Journal of Petrology, 2008, 50(1):195-196. DOI URL
[17]	VEKSLER I V, DORFMAN A M, DULSKI P, et al. Partitioning of elements between silicate melt and immiscible fluoride, chloride, carbonate, phosphate and sulfate melts, with implications to the origin of natrocarbonatite[J]. Geochimica et Cosmochimica Acta, 2012, 79:20-40. DOI URL
[18]	MCCREATH J A, FINCH A A, HERD D A, et al. Geochemistry of pyrochlore minerals from the Motzfeldt Center, South Greenland: the mineralogy of a syenite-hosted Ta, Nb deposit[J]. American Mineralogist, 2013, 98(2/3):426-438. DOI URL
[19]	LEE W J, WYLLIE P J. Experimental data bearing on liquid immiscibility, crystal fractionation, and the origin of calciocarbonatites and natrocarbonatites[J]. International Geology Review, 1994, 36(9):797-819. DOI URL
[20]	刘琰. 川西冕宁—德昌稀土成矿带霓辉正长岩-碳酸岩杂岩体成岩成矿时代[J]. 地质学报, 2015, 89(增刊):164-167.
[21]	黄智龙, 许成, 刘丛强. 碳酸岩与铂族元素地球化学[J]. 地质论评, 2005, 51(4):443-451.
[22]	李波, 黄智龙, 许成, 等. 四川冕宁稀土矿床碳酸岩PGE地球化学初步研究[J]. 矿物学报, 2007, 27(增刊1):423-429.
[23]	许成, 黄智龙, 刘丛强, 等. 四川牦牛坪稀土矿床碳酸岩地球化学[J]. 中国科学D辑: 地球科学, 2002, 32(8):635-643.
[24]	GUZMICS T, MITCHELL R H, SZABÓ C, et al. Carbonatite melt inclusions in coexisting magnetite, apatite and monticellite in Kerimasi calciocarbonatite, Tanzania: melt evolution and petrogenesis[J]. Contributions to Mineralogy and Petrology, 2011, 161(2):177-196. DOI URL
[25]	RANKIN A H, LE BAS M J. Liquid immiscibility between silicate and carbonate melts in naturally occuring ijolite magma[J]. Nature, 1974, 250(5463):206-209. DOI URL
[26]	NIELSEN T F D, SOLOVOVA I P, VEKSLER I V. Parental melts of melilitolite and origin of alkaline carbonatite: evidence from crystallised melt inclusions, Gardiner complex[J]. Contributions to Mineralogy and Petrology, 1997, 126(4):331-344. DOI URL
[27]	WEIDENDORFER D, SCHMID T, M W, MATTSSON H B. Fractional crystallization of Si-undersaturated alkaline magmas leading to unmixing of carbonatites on Brava Island (Cape Verde) and a general model of carbonatite genesis in alkaline magma suites[J]. Contributions to Mineralogy and Petrology, 2016, 171(5):1-29. DOI URL
[28]	SHISHKINA T A, BOTCHARNIKOV R E, HOLTZ F, et al. Compositional and pressure effects on the solubility of H₂O and CO₂ in mafic melts[J]. Chemical Geology, 2014, 388:112-129. DOI URL
[29]	WEIDENDORFER D, SCHMIDT M W, MATTSSON H B. A common origin of carbonatite magmas[J]. Geology, 2017, 45(6):507-510. DOI URL
[30]	SCHMIDT M W, WEIDENDORFER D. Carbonatites in oceanic hotspots[J]. Geology, 2018, 46(5):435-438. DOI URL
[31]	BLANK J G, BROOKER R A. Experimental studies of carbon dioxide in silicate melts: solubility, speciation, and stable carbon isotope behavior[J]. Reviews in Mineralogy and Geochemistry, 1994, 30(1):157-186.
[32]	BROOKER R A, KOHN S C, HOLLOWAY J R, et al. Structural controls on the solubility of CO₂ in silicate melts: Part I: bulk solubility data[J]. Chemical Geology, 2001, 174(1/2/3):225-239. DOI URL
[33]	DAWSON J B. Sodium carbonate lavas from Oldoinyo Lengai, Tanganyika[J]. Nature, 1962, 195(4846):1075-1076. DOI URL
[34]	GITTINS J. Carbonatite origin and diversity[J]. Nature, 1989, 338(6216):548. DOI URL
[35]	舒小超, 刘琰, 李德良, 等. 川西冕宁—德昌稀土矿带霓长岩的地球化学特征及地质意义[J]. 岩石学报, 2019, 35(5):1372-1388.
[36]	DAWSON J B, GARSON M S, ROBERTS B. Altered former alkalic carbonatite lava from Oldoinyo Lengai, Tanzania: inferences for calcite carbonatite lavas[J]. Geology, 1987, 15(8):765. DOI URL
[37]	GUZMICS T, MITCHELL R H, SZABÓ C, et al. Liquid immiscibility between silicate, carbonate and sulfide melts in melt inclusions hosted in co-precipitated minerals from Kerimasi volcano (Tanzania): evolution of carbonated nephelinitic magma[J]. Contributions to Mineralogy and Petrology, 2012, 164(1):101-122. DOI URL
[38]	HUANG W L, WYLLIE P J. Melting relationships in the systems CaO-CO₂ and MgO-CO₂ to 33 kilobars[J]. Geochimica et Cosmochimica Acta, 1976, 40(2):129-132. DOI URL
[39]	KJARSGAARD B, PETERSON T. Nephelinite-carbonatite liquid immiscibility at Shombole volcano, East Africa: petrographic and experimental evidence[J]. Mineralogy and Petrology, 1991, 43(4):293-314. DOI URL
[40]	LEE W J, WYLLIE P J. Processes of crustal carbonatite formation by liquid immiscibility and differentiation, elucidated by model systems[J]. Journal of Petrology, 1998, 39(11/12):2005-2013. DOI URL
[41]	TWYMAN J D, GITTINS J. Alkalic carbonatite magmas: parental or derivative?[J]. Geological Society of London Special Publications, 1987, 30(1):85-94. DOI URL
[42]	KJARSGAARD B A, HAMILTON D L, PETERSON T D. Peralkaline nephelinite/carbonatite liquid immiscibility: comparison of phase compositions in experiments and natural lavas from Oldoinyo Lengai[J]. Carbonatite Volcanism, 1995, 4:163-190.
[43]	BROOKER R A, KJARSGAARD B A. Silicate-carbonate liquid immiscibility and phase relations in the system SiO₂-Na₂O-Al₂O₃-CaO-CO₂ at 0.1-2.5 GPa with applications to carbonatite genesis[J]. Journal of Petrology, 2011, 52(7/8):1281-1305. DOI URL
[44]	VEKSLER I V, PETIBON C, JENNER G A, et al. Trace element partitioning in immiscible silicate-carbonate liquid systems: an initial experimental study using a centrifuge autoclave[J]. Journal of Petrology, 1998, 39(11/12):2095-2104. DOI URL
[45]	MARTIN L H J, SCHMIDT M W, MATTSSON H B, et al. Element partitioning between immiscible carbonatite-kamafugite melts with application to the Italian ultrapotassic suite[J]. Chemical Geology, 2012, 320/321:96-112. DOI URL
[46]	MARTIN L H J, SCHMIDT M W, MATTSSON H B, et al. Element partitioning between immiscible carbonatite and silicate melts for dry and H₂O-bearing systems at 1-3 GPa[J]. Journal of Petrology, 2013, 54(11):2301-2338. DOI URL
[47]	MITCHELL R H. Peralkaline nephelinite-natrocarbonatite immiscibility and carbonatite assimilation at Oldoinyo Lengai, Tanzania[J]. Contributions to Mineralogy and Petrology, 2009, 158(5):589-598. DOI URL
[48]	NABYL Z, MASSUYEAU M, GAILLARD F, et al. A window in the course of alkaline magma differentiation conducive to immiscible REE-rich carbonatites[J]. Geochimica et Cosmochimica Acta, 2020, 282:297-323. DOI URL
[49]	VEKSLER I V, NIELSEN T F D, SOKOLOV S V. Mineralogy of crystallized melt inclusions from Gardiner and Kovdor ultramafic alkaline complexes: implications for carbonatite genesis[J]. Journal of Petrology, 1998, 39(11/12):2015-2031. DOI URL
[50]	FOUSTOUKOS D I, MYSEN B O. The structure of water-saturated carbonate melts[J]. American Mineralogist, 2015, 100(1):35-46. DOI URL
[51]	SHIMIZU N, AKIMOTO S I. Partitioning of strontium between clinopyroxene and liquid at high pressures: preliminary experiments[J]. Earth and Planetary Science Letters, 1971, 13(1):134-138. DOI URL
[52]	SHIMIZU N. An experimental study of the partitioning of K, Rb, Cs, Sr and Ba between clinopyroxene and liquid at high pressures[J]. Geochimica et Cosmochimica Acta, 1974, 38(12):1789-1798. DOI URL
[53]	HAMILTON D L, BEDSON P, ESSON J. The behaviour of trace elements in the evolution of carbonatites[M]//BELL K. Carbonatites, genesis and evolution. London: Unwin Hyman, 1989: 405-427.
[54]	李慧, 尚林波, 樊文苓. 铜在熔体流体间分配实验的研究进展[J]. 矿物学报, 2012, 32(1):28-32.
[55]	KELLER J, SPETTEL B. The trace element composition and petrogenesis of natrocarbonatites[J]. Carbonatite Volcanism, 1995, 4:70-86.
[56]	GUZMICS T, BERKESI M, BODNAR R J, et al. Natrocarbonatites: a hidden product of three-phase immiscibility[J]. Geology, 2019, 47(6):527-530. DOI URL
[57]	郑旭, 刘琰, 欧阳怀, 等. 川西冕宁木落寨碳酸岩型稀土矿床流体演化对成矿的制约: 来自包裹体和稳定同位素的证据[J]. 岩石学报, 2019, 35(5):1389-1406.
[58]	宋文磊, 许成, 王林均, 等. 与碳酸岩-碱性杂岩体相关的内生稀土矿床成矿作用研究进展[J]. 北京大学学报(自然科学版), 2013, 49(4):725-740.
[59]	PANINA L I. Multiphase carbonate-salt immiscibility in carbonatitemelts: data on melt inclusions from the Krestovskiy massif minerals (Polar Siberia)[J]. Contributions to Mineralogy and Petrology, 2005, 150(1):19-36. DOI URL
[60]	KYNICKY J, SMITH M P, SONG W L, et al. The role of carbonate-fluoride melt immiscibility in shallow REE deposit evolution[J]. Geoscience Frontiers, 2019, 10(2):527-537. DOI URL
[61]	MITCHELL R H. Carbonate-carbonate immiscibility, neighborite and potassium iron sulphide in Oldoinyo Lengai natrocarbonatite[J]. Mineralogical Magazine, 1997, 61(409):779-789. DOI URL
[62]	GUZMICS T, ZAJACZ Z, MITCHELL R H, et al. The role of liquid-liquid immiscibility and crystal fractionation in the genesis of carbonatite magmas: insights from Kerimasi melt inclusions[J]. Contributions to Mineralogy and Petrology, 2015, 169(2):1-18. DOI URL
[63]	FENG M, SONG W L, KYNICKY J, et al. Primary rare earth element enrichment in carbonatites: evidence from melt inclusions in Ulgii Khiid carbonatite, Mongolia[J]. Ore Geology Reviews, 2020, 117:103294. DOI URL
[64]	范宏瑞, 牛贺才, 李晓春, 等. 中国内生稀土矿床类型、成矿规律与资源展望[J]. 科学通报, 2020, 65(33):3778-3793.