that some members of a petrological clan crystallized under different conditions e.g. ... The concept of a lamprophyre clan is considered to be unnecessary as.
Mineralogy and Petrology (1994) 51:137-146
Mineralogy anti Petrology © Springer-Verlag 1994 Printed in Austria
The lamprophyre facies R. H. Mitchell Department of Geology, Lakehead University, Ontario, Canada Received September 12, 1992; accepted November 26, 1992
Summary Lamprophyres are a polygenetic group of rocks that have formed by the crystallization of common magma types, including lamproites and kimberlites, under volatile-rich conditions. The term lamprophyre is considered to have no genetic significance and the recognition of a lamprophyre facies is proposed as a means of conveying the concept that some members of a petrological clan crystallized under different conditions e.g. volatile-rich, to other members of that clan. A petrological clan is defined as suite of comagmatic rocks that have been derived from a particular parental magma which has been produced repeatedly in time and space. Lamprophyres are redefined as rocks which are characterized by the presence of euhedral-to-subhedral phenocrysts of mica and/or amphibole together with lesser clinopyroxene and/or melilite set in a groundmass which may consist (either singly or in various combinations) of plagioclase, alkali feldspar, feldspathoid, carbonate, monticellite, mica, amphibole, pyroxene, perovskite, Fe-Ti oxides and glass. The concept of a lamprophyre clan is considered to be unnecessary as it has no petrogenetic significance.
Zusammenfassung Die Lamprophyr-Fazies Lamprophyre sind eine Gruppe polygenetischer Gesteine, die, einschlieBlich der Lamproite und Kimberlite, durch Kristallisation gew6hnlicher Magmentypen unter volatil-reichen Bedingungen entstehen. Der Begriff Lamprophyr wird in einem nicht genetischen Sinne verstanden. Das Erkennen einer Lamprophyr-Fazies wird als eine M6glichkeit betrachtet, dieses Konzept auf eine Kristallisation unter unterschiedlichen Bedingungen, z.B. volatil-reiche Kristallisationsbedingungen im Vergleich zu anderen Gesteinen desselben Clans, zu fibertragen. Ein petrologischer Clan wird als eine komagmatische Suite, die aus einem bestimmten Ursprungsmagma, das zeitlich und r~iumlich wiederholt produziert wurde, definiert. Lamprophyre werden als Gesteine redefiniert, die durch eu- bis subhedrale Ph/inokristalle von Glimmern und/oder Amphibolen und untergeordnet Klinopyroxen und/oder Melilith in einer Grundmasse bestehend aus einem oder mehreren der Minerale Plagioklas, Alkalifeldspat, Foiden, Karbonat, Mon-
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R.H. Mitchell ticellit, Glimmer, Amphibol, Pyroxen, Perovskit, Fe-Ti-Oxiden und Glas charakterisiert sin& Das Konzept eines Lamprophyr-Clans wird fiir unnotwendig erachtet, da ihm keine petrogenetische Bedeutung zukommt.
Introduction
Despite over 100 years of study lamprophyres remain to most petrologists one of the most obscure and least understood rock groups. Commonly, lamprophyres are treated, if at all, as an afterthought in most petrology texts by authors who merely reiterate old shibboleths and otiose terminology. Descriptions of petrological provinces or alkaline complexes tend to ignore or downplay any lamprophyric components and/or dismiss them as unimportant. Attempts to redress this situation have been made by the late Nick Rock and his single-minded promotion of "lamprophyres" as objects worthy of study must be applauded. Petrologists in general, and those in particular who study lamprophyres, kimberlites and lamproites will long be indebted to Nick Rock for making us think long and hard about the received wisdom pertaining to these interesting rocks. The term "lamprophyre" was introduced into petrological literature by Gumbel in 1874. The name is derived from the macroscopic appearance of dike rocks occurring at the type locality in Germany. These contain large biotite phenocrysts and were described by Gumbel as a "glistening porphyry" (lampros porphyros). Following its introduction the term was broadened to encompass a wide variety of hypabyssal rocks containing ferromagnesian phenocrysts (Rosenbusch, 1897). As more rocks that were difficult to classify were found in the late 19th and early 20th centuries, these were added to the lamprophyre group. Eventually the group became a repository for any difficult to characterize mafic phenocryst-rich rock. Unfortunately, the practice of type locality nomenclature led to the introduction of a "legion of obscure rock types named after equally obscure European villages" (Rock, 1990, p. 1). This archaic, commonly imprecise, nomenclature has been a particular hinderance in lamprophyre petrogenetic studies as rocks of diverse parentage became grouped under one petrographic banner. This grouping has been interpreted to imply genetic relationships where none actually exist. During the past decade interest in lamprophyres has been rekindled because of their importance as windows into the deep mantle and supposed association with diamonds and gold deposits. Rock (1986, 1990) has even linked lamprophyres, kimberlites and lamproites into a super-group of rocks termed the "lamprophyre clan". This concept has been vigorously opposed by Mitchell (1992) and Mitchell and Bergman (1991) on the grounds that linking rocks which are genetically different serves no petrological purpose. It will be shown in this paper that: (1) the lamprophyre clan is a misnomer; (2) members of the clan are genetically unrelated; and (3) the clan merely unites rocks which have crystallized under volatile-rich conditions.
The lamprophyre elan--do we need it?
To answer this question one needs to understand Rock's (1990) use of the term "clan". He used it to refer to a group of rocks that superficially look the same, are commonly associated in the field and have a number of petrological characteristics
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in common, e.g. richness in volatiles, porphyritic texture, occurrence as minor intrusions. A lamprophyric character commonly implies the presence of mica, amphibole or pyroxene phenocrysts set in glassy or felsic matrix. Kimberlites and lamproites are included in the "lamprophyre clan" by both Rock (1990) and LeMaitre et al. (1989) because they are considered to have lamprophyric characteristics. Although some varieties of kimberlite and lamproite indeed have lamprophyric characteristics, most members of the group are devoid of such characteristics. Thus, the majority of the monticellite-serpentine calcite or isotopic group 1 kimberlites do not contain phlogopite, amphibole or pyroxene phenocrysts, or have a felsic groundmass (Mitchell, 1986). The presence of olivine macrocrysts and/or phenocrysts does not confer a lamprophyric character unless the meaning of the term is even further broadened to include any olivine-phyric rock. Some isotopic group 1 or archetypal kimberlites (Mitchell, 1992) do contain macrocrystal mica. Concentration of this mica by flow differentiation or other processes may confer a lamprophyric character to some kimberlites. However, these rocks are typically only minor members of a spectrum of consanguineous non-lamprophyric rocks. Extension of the lamprophyric designation of minor members of the group to describe the whole group is totally unwarranted. Isotopic group 2 kimberlites are not separated by Rock (1990) or LeMaitre et al. (1989) from archetypal isotopic group 1 kimberlites. The former rocks typically have a lamprophyric character due to the occurrence in them of abundant macrocrystal and phenocrystal phlogopite. It was this feature, but more importantly the presence in them of diamond, which led Wagner (1914) to term them micaceous or lamprophyric kimberlite. Recently, Mitchell(1992) and Mitchell and Bergman (1991) have argued that these rocks are derived from a unique variety of potassic magmatism as they are mineralogically totally unlike archetypal kimberlites. The rocks are thus termed orangeites (Mitchell, 1992), to recognize this distinctiveness. Their parent magmas are unrelated to those of archetypal kimberlites and apparently unique to the Kaapvaal craton. Thus, Mitchell and Bergman (1991) and Mitchell (1992) consider that these rocks cannot be "lamprophyric kimberlites" and Rock (1990) and LeMaitre et al. (1989) are incorrect in believing them to be a variety of bona-fide kimberlite. Regardless of the name i.e. group 2 kimberlites or orangeites, these rocks are not members of Rock's (1990) lamprophyre clan. Lamproites are even more unsuited to be members of the "lamprophyre clan" than kimberlites, as many of them do not meet the basic criteria required for inclusion in the "clan". This is because lamproites commonly contain felsic phenocrysts, such as sanidine and leucite. In common with kimberlites not all members of a given lamproite petrological province have lamprophyric character. For example, diopside-leucite lamproites are not lamprophyric in the commonly used sense of the term. It is correct however to state that phlogopite-rich members of a lamproite petrological province do have lamprophyric character. Turning to the type of lamprophyres recognized by Rosenbusch (1897) it is instructive to consider the alkaline lamprophyres, these being the commonest and therefore best understood varieties. It has long been known that camptonites and monchiquites are intimately and genetically associated with alkali basaltic magmatism. This association has been recognized by the use of the term "anchibasalt" by Wimmenauer (1973) to describe them. Alkaline lamprophyres are regarded by
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many petrologists e.g. Clarke et al. (1983) as rocks which are the products of the prolonged crystallization of basaltic magma. If we were to follow Rock's arguments as applied to kimberlites and lamproites we should have to include in the "lamprophyre clan" all consanguineous nonlamprophyric rocks. However, it is extremely unlikely that any petrologist would refer to a gabbro or basalt as lamprophyre. It is this illustration that demonstrates the futility of recognizing a "lamprophyre clan", as logically it will, by extension of the argument to other varieties of lamprophyres, eventually include all igneous rocks. The principal point of the above discussion is that rocks belonging to well defined co-magmatic suites include types which may be described as having lamprophyric features. There is no valid petrogenetic reason for isolating these rock types from their consanguineous antecedents or descendants and grouping them in some non-genetic super clan. Even Rock (1990) notes that members of his "lamprophyre clan" have distinct origins. Mitchell (1992) has stressed that the object of rock classification should ultimately be an aid in determining the origin of a given rock. If classifications have no genetic significance then they serve no useful petrogenetic purpose. Thus, Mitchell (1992), Mitchell and Bergman (1991), and this paper, question the value of a grouping that has absolutely no petrogenetic significance.
Clans and facies
The term "clan" has been used very loosely in igneous petrology. The concept was introduced by Scottish petrologists, and popularized by the influential American petrologist Reginald Daly (1914), to refer to rocks which formed by the differentiation and crystallization of particular magma types. Rocks of diverse modal character and chemical composition may be included in such a clan as they are genetically related. Clan as used in this sense is synonymous with co-magmatic or consanguineous series. Rock (1990) uses the term "clan" to refer to a group of rocks that are united by a common trait and are not genetically related (see above). Standard reference works give yet another definition i.e. a group of igneous rocks that are closely related in chemical composition (AGI Glossary of Geology; Encyclopedia of Igneous and Metamorphic Petrology). This definition is particularly unsatisfactory as it has no petrogenetic significance, as rocks that are closely related in composition may be simply heteromorphs. Rocks which belong to a co-magmatic series are certainly not closely similar in composition e.g. olivine lamproite and sanidine richterite lamproite are both members of the lamproite clan. Mitchell (1992) has recommended that the term clan be used only according to its original meaning i.e. actual or purported descent from a common ancestor. A petrological clan is thus defined as "a group of rocks derived from a particular type of parental magma which has been produced repeatedly in time and space. Individual petrological provinces are composed of co-magmatic or consanguineous rocks derived from specific batches of this magma type". Note that according to this definition there cannot be a "lamprophyre clan" as there is no "lamprophyre magma type".
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The facies concept has been used for many years by metamorphic and sedimentary petrologists, but has only recently been extensively utilized by some igneous petrologists e.g. Cas and Wright (1987); Clement and Skinner (1985). Cas and Wright (1987, p. 5) define a facies as "a body or interval of rock or sediment which has a unique definable character that distinguishes it from other facies or intervals of rock or sediment". The definable character may be any property, texture or modal mineralogy that serves to set the rock apart from other rocks. Using this definition it may be appreciated that Rock's (1990) "lamprophyre clan", which unites rocks sharing a common trait, is in reality, an example of the facies concept.
Lamprophyric facies From the above discussion it is suggested that the adjective "lamprophyric" be used to describe a facies of rocks derived from particular parent magma. This usage emphasizes the concept that some members of a petrological clan of co-magmatic rocks may have crystallized under different conditions to other members of that clan. This usage retains the original meaning of "lamprophyric" and simply describes the common observable characteristics of a particular group of rocks that sets them apart from other associated rocks. Recognition of a lamprophyric facies does not imply that we know how rocks belong to the facies originated. However, recognition of the facies ultimately has genetic significance as it serves to draw to our attention rocks that must have _formed by specific and/or different process to other members of the co-magmatic suite. In this context sannaites, camptonites and monchiquites may be described as rocks of the lamprophyric facies of the alkali olivine basalt clan. Other rocks of non-lamprophyric aspect belonging to the clan would represent other facies e.g. basalts and akaramites of the extrusive facies or gabbros and pyroxenites of the plutonic facies. Applying the concept to archetypal or isotopic group 1 kimberlites it is possible now to recognize a lamprophyric facies of these rocks, in cases where differentiation processes (unspecified) have led to high modal concentrations of phlogopite. Such rocks may be referred to as phlogopite monticellite kimberlites of the hypabyssal lamprophyric facies. Further examples of the facies concept applied to lamproites and orangeites are given in Mitchell (1992). Lamprophyres have traditionally been thought of as being minor hypabyssal intrusions. However, there are many well documented significant examples of both extrusive and plutonic lamprophyric rocks. Examples of lamprophyric extrusive rocks include the Eocene minette lavas of the Colima graben, Mexico (Luhr and Carmichael, 1981) and the Early Proterozoic ultrapotassic lavas of the Baker Lake group, North West Territories (Peterson, 1992). The latter occurrence is especially significant as the lavas are particularly voluminous (10,000 kin3). These lavas and the occurrence elsewhere of regional lamprophyric dike swarms (Rock, 1990), which presumably were feeders to lavas, indicate that extrusive lamprophyric magmatism is more important than commonly realized. Plutonic lamprophyres include such rocks as biotite pyroxenite, uncompahgrite, turjaite, okaite, appinite and vaugnerite. Phlogopite and hornblende in these rocks are not present as phenocrysts but are typically present in sufficiently large quan-
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tities that they confer a macroscopic lamprophyric appearance to the rocks. The rocks are commonly associated with hypabyssal lamprophyres of similar modal mineralogy e.g. aln6ites with okaites, appinites with spessartites and vogesites. In some instances lamprophyric dikes can be shown to have originated from plutonic lamprophyric intrusions e.g. spessartites from appinites (Rock, 1990), aln6ites from melilitoids (Ulrych et al. 1988). These relationships demonstrate that the plutonic volatile-rich rocks named above are bona-fide members of the lamprophyre facies. It is beyond the scope of this work to discuss the question of whether the names should be retained or replaced by compound names reflecting their magmatic heritage. Clearly, plutonic lamprophyres represent the products of crystallization of volatile-rich magmas retained in magma chambers. Hypabyssal and volcanic lamprophyric rocks originate from these magma chambers and record stages in the long term evolution of the chamber. Hybridization and crystallization in these environments account for the petrological complexities of lamprophyres i.e. resorbed and complexly zoned crystals and non-equilibrium mineral assemblages.
Lamprophyre defined Lamprophyres are a diverse group of polygenetic rocks united by the common trait of crystallization under volatile-rich conditions. Because of the diverse mineral assemblages which may crystallize from these magmas, it is not possible to devise a succinct and short definition of the term. The definition proposed by Rock (1990, p.17) is unsatisfactory as it unites many of the mineralogical characteristics of kimberlites and lamproites with those of Rosenbusch-defined lamprophyres. Compositional and geological data are also included in Rock's (1990) definition. The former are not immediately observable and the latter are undesirable in a petrological definition. As an alternative, an extended definition that highlights the principal characteristics of the group in terms of the facies concept has been proposed by Mitchell (1992). This states that: Lamprophyres are rocks which are characterized by the presence of euhedralto-subhedral phenocrysts of mica and/or amphibole together with lesser clinopyroxene and/or melilite set in a groundmass which may consist (either singly or in various combinations) of plagioclase, alkali feldspar, feldspathoids, carbonate, monticellite, melilite, mica, amphibole, pyroxene perovskite, Fe-Ti oxides and glass. This definition is presented as a starting point for further discussion. Limits for the modal quantities of the minerals present e.g. phenocrystal clinopyroxene and melilite, are purposely not specified, as this aspect of lamprophyre classification is beyond the scope of this paper. Olivine is not included in the above definition because it is ubiquitous in lamprophyres and its presence is not indicative of unusual conditions of crystallization. Traditionally, olivine has never been considered to be a diagnostic mineral for recognizing lamprophyres e.g. Hatch et al. (1961) and there do not appear to be any compelling petrological grounds for abandoning this viewpoint. The status of the term "hornblendite" requires clarification as a given lamprophyric rock may vary in its mode from "hornblendite" (i.e. M > 90) to hornblendebearing (i.e. M < 90).
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A characteristic feature of lamprophyres is the presence of a hydrous phenocrystal assemblage. However, it should be realized that rocks containing these minerals may be modally gradational into rocks lacking them. Thus, aln6ites may grade into pyroxene-calcite rocks by a decrease in the amount of phlogopite and melilite. Panidiomorphic textures are common in lamprophyres but are not characteristic. Many lamprophyres have mineralogical characteristics e.g. reversely zoned, oscillatory zoned and/or resorbed phenocrysts, high modal abundances of phenocrysts etc., which indicate that they do not represent liquid compositions. In these cases the bulk chemical composition results from the mixing or hybridization of several batches of magma and/or fragmented cumulates derived from the same parental magma. Lamprophyres develop as a consequence of retention of volatiles in the parent magma either by crystallization at high pressure or by prolonged normal differentiation processes. However, it is especially important to realize that there is no common mechanism involved in their genesis. Recognition of a lamprophyric facies implies that each lamprophyre must be considered in the context of the genesis and evolution of its parental magma type. There is no petrological reason to consider all lamprophyres together as is customary in many texts. Thus, for example the petrogenesis of camptonites and monchiquites should be discussed only in the context of their derivation from alkali olivine basalts, basanites or nephelinites and that of aln6ites only with respect to melilititic magmas.
Lamprophyre nomenclature Realization that lamprophyres are nothing more in many instances than the hydrous crystallization products of common magma types will ultimately lead to a reconsideration of their nomenclature. Revision of lamprophyre nomenclature is required as many of the currently-used terms are imprecisely formulated and/or are uninformative type locality names. Use of genetic classifications of the type employed for kimberlites (Skinnner and Clement, 1979; Mitchell, 1986) or lamproites (Scott Smith and Skinner, 1984; Mitchell and Bergman, 1991) together with the recognition of a lamprophyric facies could simplify the nomenclature of many lamprophyres. Detailed discussion of revisions to lamprophyre nomenclature are beyond the scope of this paper and are currently the subject of discussions by a subcommittee of the IUGS Subcommission on the Systematics of Igneous Rocks. The nomenclature of the lamprophyric facies of the melilitite clan is in particular need of revision. These rocks are bedeviled with such names as aln6ite, aillikite, vesecite, polzenite, modlibovite, bergalite etc. The rocks consist of varying modal amounts of olivine, phlogopite, melilite, monticellite, calcite, clinopyroxene, serpentine, calcite, perovskite and spinel. Many of these rocks have been broadly classified as ultramafic lamprophyres by Rock (1990). They are typically found as minor intrusions associated with alkaline rock-carbonatite complexes. Von Eckerman's (1948) description of the dikes associated with the Aln6 complex illustrates the deficiencies of the existing nomenclature, as fourteen names are applied to a consanguineous suite of modally diverse dikes.
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In a genetic classification, compound names would eliminate the archaic nomenclature and recognize modal variants of a single lamprophyric facies of the melilitite clan. A suitable stem name indicating the nature of the parental magma has not yet been agreed upon. Mitchell (1992) has suggested that the acronym "melnoite" be used for this facies as it is devoid of the petrographic connotations associated with any of the existing names. Thus, in a revision to the nomenclature, aln6ites would become melilite diopside phlogopite melnoite; aillikite, olivine phlogopite calcite melnoite. The other more obscure names could be similarly eliminated. This nomenclature permits the recognition of modal variations in the hypabyssal lamprophyric facies of the melilitite clan that are obscured by the type locality nomenclature. Minettes provide another example of the inadequacies of the current nomenclature of lamprophyres. Minettes are defined by Rock (1990) as "consisting of phenocrysts of phlogopite-biotite, with or without subordinate calcic or alkali amphibole, forsteritic olivine or diopsidic clinopyroxene set in a groundmass of the same plus alkali feldspar and subordinate plagioclase". This definition is so broad that a wide variety of rocks may be described as minettes. Hence, rocks associated with calcalkaline volcanism (Luhr and Carmichael, 1981), lamproites (Rock et al., 1992) and mafic phonolites (O'Brien et al., 1991) have all been termed minettes. As the magma types involved in the genesis of these diverse "minettes" undoubtedly are not genetically related it would seem unreasonable to suppose that all of these "minettes" are mineralogieally similar. Although there may be gross similarities in the major modal mineralogy of these diverse "minettes" there will be significant differences in the accessory mineral assemblage and in the composition of the major minerals that serve to distinguish between phlogopite--alkali feldspar-rich rocks derived from diverse parental magmas. The term °'minette" must be redefined or restricted to use in its original sense for rocks associated with calc-alkaline plutonism and volcanism. Other rocks described as minettes may be classified according to textural-genetic classifications (Mitchell, 1992). Thus, the "minettes" of Rock et al. (1992) may be referred to as phlogopite-sanidine lamproite to reflect the nature of their parent magma (Mitchell and Bergman, 1991). This designation indicates that the rocks are a lamprophyric facies of the lamproite clan. Conclusion
In conclusion, this paper argues that there is no compelling petrogenetic need for the recognition of a "lamprophyre clan". It is recognized that there is indeed a group of polygenetic rocks which may be united by common trait i.e. lamprophyric character. However, it is argued that this group is better described as a facies. Thus, it is recommended that the term "lamprophyre clan" be replaced by "lamprophyric facies". Recognition of a lamprophyric facies enables the work of Rock (1990) to be used to distinguish between the different types of lamprophyric facies rocks. The object of classification is ultimately to understand the petrogenesis of rocks. I believe that classifications should have a genetic basis if we are to make any progress in this respect, as non-genetic classifications lead to incorrect petrogenetic speculation. Genetic classifications of the type advocated by Mitchell (1992), Mitchell and Bergman (1991) and Scott Smith and Skinner (1984) do not claim that the origins of a particular rock are understood. These classifications simply serve to
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place rocks within a co-magmatic series or identify the parental m a g m a type. Application of this approach to the nomenclature of lamprophyres will eventually rationalize their nomenclature and eliminate the existing archaic terminology.
Acknowledgements
This research on the petrogenesis of alkaline rocks is supported by the Natural Sciences and Engineering Research Council of Canada and Lakehead University. Many of the ideas expressed in this paper have stemmed from discussions with the late Nick Rock. It is regretted that Nick cannot rebut some of the arguments advanced in this paper. Members of the lUGS working group on the nomenclature of kimberlites, lamproites and lamprophyres are thanked for comment and criticism of many of my ideas concerning nomenclature. A. D. Edgar, M. J. LeBas and W. R. Taylor are thanked for reviews of an earlier version of this paper.
References
Cas RAF, Wright JV (1987) Volcanic successions: modern and ancient. Allen and Unwin, London Clarke DB, Muecke GK, Pe-Piper G (1983) The lamprophyres of Ubekendt Ejland, West Greenland: products of renewed partial melting or extreme differentiation? Contrib Mineral Petrol 83:117-127 Clement R, Skinner E M W (1985) A textural genetic classification of kimberlites. Trans Geol Soc S Africa 88:403-409 Daly R (1914) Igneous rocks and their origin. Hafner Publishing, New York Gumbel CW Von (1874) Die palfiolithischen Eruptivgesteine des Fichtelgeberges. Franz, Munich Hatch FH, Wells AK, Wells M K (1961) Petrology of the igneous rocks. T Murby & Co, London LeMaitre RW, Bateman P, Dubek A, Keller J, Lameyre J, LeBas M J, Sabine PA, Schmid R, Sorensen H, Streckeisen A, Wolley AR, Zanettin B (1989) A classification of igneous rocks and glossary of terms. Blackwell, Oxford Luhr JF, Carmichael ISE (1981) The Colima volcanic complex, Mexico, part II. Late Quaternary cinder cones. Contrib Mineral Petrol 76:127-147 Mitchell RH (1986) Kimberlites: mineralogy, geochemistry and petrology. Plenum Publishing, New York - - - - (1992) Suggestions for revisions to the terminology of kimberlites and lamprophyres from a genetic viewpoint. Proc 5th Internat Kimberlite Conf (in press) Bergman SC (1991) Petrology of lamproites. Plenum Publishing, New York O'Brien HE, Irving A J, MeCallum IS (1991) Eocene potassic magmatism in the Highwood Mountains, Montana: petrology, geochemistry and tectonic implications. J Geophys Res 96:13237-13260 Peterson TD (1992) Early Proterozoic ultrapotassic volcanism of the Keewatin Hinterland, Canada. Proc 5th Internat Kimberlite Conf (in press) Rock NMS (1986) Kimberlites as varieties of lamprophyres: implications for geological mapping, petrological research and mineral exploration. In: Ross et al. (eds) Proc 4th Internat Kimberlite Conf Blackwell Publications 1:528-544 - - - - (1990) Lamprophyres. Blackie and Son Ltd, London - - - - Griffin B J, Edgar AD, Paul DK, Hergt JM (1992) A spectrum of potentially diamondiferous lamproites and minettes from the Jharia coalfield, eastern India. J Volcan Geotherm Res 50:55-83 -
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Rosenbusch H (1897) Mikroscopische Physiographie, 3. Aufl. Schweizerbart, Stuttgart Scott Smith BH, Skinner E M W (1984) A new look at Prairie Creek, Arkansas. In: Kornprobst J (ed) Kimberlites I. Kimberlites and related rocks. Elsevier, Amsterdam, pp 255-284 Skinner EMW, Clement CR (1979) Mineralogical classification of South African kimberlites. In: Boyd FR, Meyer HOA (eds) Proc 2nd Internat Kimberlite Conf. 1. Kimberlites, Diatremes and Diamonds: Their Geology, Petrology and Geochemistry. Am Geophys Union, Washington, pp 129-139 Ulrych J, Povondra R, Rutsek J, Pivec E (1988) Melilitie and melilite-bearing subvolcanic rocks from the Plouenice River region, Czechoslovakia. Acta Universitatis CarolinaeGeologica 2:195-231 Von Eckermann H (1948) The alkaline district of Alno Island. Sveriges Geol Undersok Ser Ca 36 Wagner PA (1914) The diamond fields of South Africa. Transvaal Leader, Johannesburg Author's address: R. H. Mitchell, Department of Geology, Lakehead University, ThunderBay, Ontario, Canada P7B 5El.
