Venezuela kimberlites

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doi: 10.1016/0377-0273(92)90039-G
Authors:Nixon, Peter H.; Davies, Gareth R.; Rex, David C.; Gray, Alan
Author Affiliations:Primary:
University of Leeds, Department of Earth Sciences, Leeds, United Kingdom
Other:
University of Leeds, United Kingdom
Volume Title:Essays on magmas and other earth fluids; a volume in appreciation of Prof. Peter G. Harris
Volume Authors:Cox, K. G., editor; Baker, P. E.
Source:Essays on magmas and other earth fluids; a volume in appreciation of Prof. Peter G. Harris, edited by K. G. Cox and P. E. Baker. Journal of Volcanology and Geothermal Research, 50(1-2), p.101-115. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0377-0273
Publication Date:1992
Note:In English. 30 refs.; illus., incl. 4 tables, sketch maps
Summary:Recently discovered kimberlitic dykes and sills in the Guaniamo area of Bolivar province (Guyana craton) are the source of nearby extensive alluvial diamonds occurring in Recent gravels and in the Roraima sedimentary group (approx 1700 m.y.) to the S. The intrusives are altered to nontronite and saponite but texturally are identified as Group I macrocrystic olivine-rich kimberlites with identifiable monticellite and phlogopite. The REE show steep patterns and high (La/Yb)n up to 480; Cr, Ni and Nb are enriched, but LILE and Ti, Zr depleted with respect to average kimberlite, partly as a result of weathering. Leached samples yield a Rb-Sr isochron age of 1732 +- 82 m.y., making them the oldest kimberlites on record. Sr and Nd isotope data are more consistent with a Group II, rather than a Group I kimberlite paragenesis. Discrete nodules which typify Group I kimberlites have not been identified. Mantle xenocrysts of Cr-rich pyropes and spinels, similar to those from cratonic harzburgite xenoliths of diamond facies, are abundant, the spinels showing metasomatic alteration to yimengite. The kimberlites are intruded by micaceous dykes enriched in K, Ba, Sr, Zr and F, indicative of a second phase of alkaline igneous activity. These igneous and metasomatic events are discussed in the context of the evolution of the Guyana craton. [R.E.S.]
Subjects:Absolute age; Archean; Dates; Diamond deposits; Dikes; Igneous rocks; Intrusions; Kimberlite; Mantle; Mineral composition; Petrography; Precambrian; Processes; Proterozoic; Rb/Sr; Sills; Sm/Nd; Ultramafic composition; Upper Precambrian; Guiana Shield; South America; Venezuela; Guaniamo Venezuela
Coordinates:N040000 N080000 W0590000 W0660000
Abstract Numbers:93M/1061
Record ID:1996025115
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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