The provenance of Borneo's enigmatic alluvial diamonds: A case study from Cempaka, SE Kalimantan

Abstract

Gem-quality diamonds have been found in several alluvial deposits across central and southern Borneo. Borneo has been a known source of diamonds for centuries, but the location of their primary igneous source remains enigmatic. Many geological models have been proposed to explain their distribution, including: the diamonds were derived from a local diatreme; they were brought to the surface through ophiolite obduction or exhumation of UHP metamorphic rocks; they were transported long distances southward via major Asian river systems; or, they were transported from the Australian continent before Borneo was rifted from its northwestern margin in the Late Jurassic. To assess these models, we conducted a study of the provenance of heavy minerals from Kalimantan's Cempaka alluvial diamond deposit. This involved collecting U-Pb isotopic data, fission track and trace element geochemistry of zircon as well as major element geochemical data of spinels and morphological descriptions of zircon and diamond. The results indicate that the Cempaka diamonds were likely derived from at least two sources, one which was relatively local and/or involved little reworking, and the other more distal which records several periods of reworking. The distal diamond source is interpreted to be diamond-bearing pipes that intruded the basement of a block that: (1) rifted from northwest Australia (East Java or SW Borneo) and the diamonds were recycled into its sedimentary cover, or: (2) were emplaced elsewhere (e.g. NW Australia) and transported to a block (e.g. East Java or SW Borneo). Both of these scenarios require the diamonds to be transported with the block when it rifted from NW Australia in the Late Jurassic. The local source could be diamondiferous diatremes associated with eroded Miocene high-K alkaline intrusions north of the Barito Basin, which would indicate that the lithosphere beneath SW Borneo is thick (~ 150 km or greater). The 'local' diamonds could also be associated with ophiolitic rocks that are exposed in the nearby Meratus Mountains. Gem-quality diamonds have been found in several alluvial deposits across central and 27 southern Borneo. Borneo has been a known source of diamonds for centuries, but the 28 location of their primary igneous source remains enigmatic. Many geological models 29 have been proposed to explain their distribution, including: the diamonds were 30 derived from a local diatreme; they were brought to the surface through ophiolite 31 obduction or exhumation of UHP metamorphic rocks; they were transported long 32 distances southward via major Asian river systems; or, they were transported from the 33 Australian continent before Borneo was rifted from its northwestern margin in the 34 Late Jurassic. To assess these models, we conducted a study of the provenance of 35 heavy minerals from Kalimantan's Cempaka alluvial diamond deposit. This involved 36 collecting U-Pb isotopic data, fission track and trace element geochemistry of zircon 37 as well as major element geochemical data of spinels and m...

An integrated study of geochemistry and mineralogy of the Upper Tukau Formation, Borneo Island (East Malaysia): Sediment provenance, depositional setting and tectonic implications

“…It supports that the tin bearing granitoids were one of the major possible sources for the sediments of Crocker-Rajang accretionary complex. Identification of the Schwaner Mountains and peninsular Main Range as source rocks for the sedimentary rocks of central Borneo and their subsequent recycling for the Neogene deposits of northern Borneo is in agreement with the previous studies by Van Hattum et al (2003Hattum et al ( , 2013 and White et al (2016).…”

“…Ages of these plutons range from 130±2.8 Ma to 77.4±1.7 Ma (Williams et al, 1988;Van Hattum et al, 2006;Witts et al, 2012;Li et al, 2015). According to White et al (2016) (Ng et al, 2015). According to the same authors, a progressive westward younging trend was apparent across the Eastern province and it was less obvious in the Main Range province.…”

“…However, heavy mineral assemblages are better indicators of provenance compared to the whole rock chemistry as the major and trace element distributions are controlled by multiple and complex mineralogical associations (Mange and Maurer, 1992;Ratcliffe et al, 2007;Sevastjanova et al, 2012). Similarly, chemistry of different heavy mineral grains has also been used to infer provenance of different sedimentary basins (Henry and Guidotti, 1985;Morton, 1991;Asiedu et al, 2000;Weltje and Von Eynatten, 2004;Mange and Morton, 2007;Meinhold et al, 2009;Stern and Wagreich, 2013;Baxter et al, 2016;White et al 2016). For example, presence of tourmaline indicates granite, granite pegmatite, contact and regionally metamorphosed rocks as the possible provenance.…”

Tectonic evolution of Sundaland

“…Separation of these Palaeozoic Cathaysian elements from core SW Borneo led Hall et al (2008), Hall (2009a, 2009b and Metcalfe (2011aMetcalfe ( , 2011b to propose that SW Borneo was derived from NW Australia in the Jurassic. Diamonds occurring in SW Borneo placer deposits without any apparent local source, have geochemical and isotope signatures similar to Australian diamonds (Taylor et al, 1990;Smith et al, 2009;Nico Kueter et al, 2016;White et al, 2016) which would support such a proposition. Van Leeuwen (2014) reviews diamond occurrences in Sundaland and suggests various possible models for the origin of Kalimantan diamonds, including fluvial derivation from mainland Sundaland during the Mesozoic.…”

A Triassic to Cretaceous Sundaland–Pacific subduction margin in West Sarawak, Borneo

“…Alluvial diamonds reported from southern Borneo resemble diamonds from NW Australia (Taylor et al, 1990) and were interpreted by White et al (2016) to be derived from the Australian margin of Gondwana.…”