Some notes on the IUGS classification of lamprophyric rocks

Abstract

The lamprophyric rocks are uncommon volatile-rich melanocratic porphyritic rocks which contain only mafic phenocrysts. The felsic minerals are confined in the groundmass. They occur as dikes, sills and diatremes. The lamprophyric rocks are sometimes associated with diamond deposits. This review article discusses the ongoing debate in igneous petrology regarding the classification of lamprophyric rocks, specifically the Lamprophyre clan vs Lamprophyre facies problem. The background of this debate is rooted in conflicting interpretations of the classification of these rocks, with some researchers grouping them into a super-group called the “Lamprophyre clan” while others emphasize the distinction between the different types of these rocks (Lamprophyre facies). The aim of this study is to provide a comprehensive analysis of relevant literature and propose a more inclusive petrological classification system for lamprophyric rocks by considering the geological setting, petrography, texture, mineralogy, whole-rock geochemistry and isotopic analysis of the various kimberlites, orangeites, lamproites, para-lamproites, calc-alkaline, alkaline and ultramafic lamprophyres. Lastly, the diamond potential is also taken into account. The implications of this study are significant for the international geological community. It proposes the adoption by the IUGS TGIR of both the Lamprophyre clan (as updated by Kamvisis & Phani, 2022, i.e. genetically interrelated rocks) and Lamprophyre facies (as suggested by Mitchell, 1994, i.e. rocks that formed under volatile-rich conditions) concepts to achieve a more widespread consensus among igneous petrologists. Both terms can be correct but they represent different perspectives in the study of these exotic rocks.

Keywords

• iugs
• classification
• kimberlite
• lamproite
• lamprophyre