The genesis of Colombian emeralds: a restatement

Abstract

A renewal of metallogenetical studies of Colombian emerald deposits produced new geological and geochemical data that favour a hydrothermal-sedimentary genetic model for these deposits. A comprehensive model is presented which integrates both chemical and structural aspects and invalidates some aspects of the model recently presented by Ottaway et al. The deposits result from a two-stage process in which shortening tectonics affect the two borders of the Eastern Cordillera of Colombia and provoke decollement planes, thrusting, and thrust-fault related folds in the Early Cretaceous black shale series. Three major descriptive and interpretative aspects of the deposits are presented: (1) time relationships between the two different sets of barren and mineralized extensional veins; (2) the association of graphite and emerald mineralization, and (3) the thermochemical sulfate reduction reaction acting at the site of the emerald deposits to reduce sulfate of evaporitic origin from the hydrothermal brines into hydrogen sulfide by interaction with organic-rich strata.Emerald is one of the most famous exports from Colombia. Even though miners from the mines of Chivor, Muzo or Coscuez recognize from experience the signs of mineralization, no comprehensive genetic model able to explain these mineralizations had been elaborated (Sutill 1994). Following our original paper in Mineralium Deposita in 1990(Giuliani et al. 1990), Ottaway et al. (1994 proposed a model for the formation of the Colombian emeralds, based on the characteristics of the Muzo deposit. This model, rather than elucidating the process of formation of Colombian emeralds, adds some confusion to it. Based on our field and laboratory practise of Colombian emerald deposits, we develop several arguments here against some major points of Ottaway et al. (1994), and we propose a comprehensive model that integrates both chemical and structural aspects.

Geology of Corundum and Emerald Gem Deposits: A Review

“…An idealized Type IA (tectonic-magmatic-related The deposits are unusual because there is no evidence of magmatic activity. Instead, the emeralds formed as a result of hydrothermal growth associated with tectonic activity (Ottaway et al, 1994;Giuliani et al, 1995;Cheilletz and Giuliani, 1996;Branquet et al, 1999a,b). The parent fluids are thought to have formed at depth from meteoric and formational water interacting with salt beds and evaporitic sequences (Ottaway et al, 1994;Giuliani et al, 2000).…”

Influence of salt in the tectonic development of the frontal thrust belt of the eastern Cordillera (Guatiquía area, Colombian Andes)

“…SAA18 Interpretation / November 2015 restricted in outcrop (e.g., in the Upín salt mine and La Campana salt layers west of Restrepo, Figure 1, and the emerald-bearing evaporitic layers of Chivor, Gachala and El Toro;Cheilletz and Giuliani, 1996;Branquet et al, 2002;Mora et al, 2009).…”

“…In the Guateque-Medina area, north of the study area, a brecciated evaporitic layer below the Macanal Formation hosts emeralds and gypsum deposits ( Figure 6) (Cheilletz and Giuliani, 1996;Branquet et al, 2002), in which fluid-inclusion studies revealed Na-Ca-K-bearing hypersaline chlorine brines responsible for emerald and pyrite crystallization by deep-seated formation waters heated by burial, thereafter dissolving evaporites by interaction with salt diapirs (Giuliani et al, 1995).…”

Source Rocks for the Giant Puguang Gas Field Sichuan Basin: Implication for Petroleum Exploration in Marine Sequences in South China

“…There are three end-member genetic types of solid bitumens, solid bitumens from biodegradation and oxidation of crude oils (Tissot and Welte, 1984), solid bitumens from thermal cracking of crude oils (Hunt, 1996;Isaksen, 2004) and solid bitumens from thermochemical sulfate reduction (Sassen, 1986;Heydari, 1997;Machel, 1987Machel, ,2001Leventhal, 1990;Cheilletz and Giuliani, 1996;Giuliani et al, 2000). The LSLR bitumens in the nonmarine sandstone reservoirs in the Xujiahe Formation most probably resulted from the thermal cracking of crude oils, whereas the HSHR bitumens in the marine carbonate reservoirs were the combined product of thermal cracking of crude oils and thermochemical sulfate reduction, and should be considered to be pyrobitumens (Sassen, 1986).…”