Multistage Sedimentary and Metamorphic Origin of Pyrite and Gold in the Giant Sukhoi Log Deposit, Lena Gold Province, Russia

Abstract

Gold mineralization at Sukhoi Log in eastern Siberia is hosted in a deformed Neoproterowic organic -bear ing and pyritic black shale and siltstone sequence that is folded into a tight overturned anticline, The deposit contains about 30 million ounces of gold at an average grade of 2.0 glt Au and is one of the largest known un developed gold resources, The high-grade gold zone forms a gently dipping tabular body in the core of the anticline , The best gold grades occur in narrow, bedding-parallel pyrite-quartz veinlets that have been folded during the main deformation event. Lower grade gold is associated with disseminated pyrite developed in and around the high-grade core of the deposit.Detailed paragenetic studies of the mineralization and host rocks havedefined six stages of pyrite develop ment in the carbonaceous sediments, The two earliest forms of pyrite, termed Pyl and PY2, are commonly developed in stratiform layers of micron-sized crystals, framboids and fine euhedra, which are interpreted as synsedimentary to early diagenetic in origin, Coarser grained, bedding-parallel aggregates of inclusion-rich pyrite , termed PY3, contain inclusions of arsenopyrite, native gold and gold tellurides and are interpreted to form during late diagenesis and earliest deformation, Coarse euhedral pyrite, PY4, overgrows the earlier pyrite (PYJ, PY2, and PY3), and the slaty cleavage developed in the host rocks, indicating a syndeformation timing, Late stage, inclusion-free pyrite, pys, overgrows and replaces earlier sulfides and is considered to be syn-to late deformation, Laser-ablation inductively coupled plasma mass spectrometry (LA-ICPMS) analyses of the various pyrite types indicate that the synsedimentary Pyl contains the highest levels of invisible gold, varying from 0.4 to 12,1 ppm, with a mean of 3,22 ppm Au, and 1,900 ppm As, Py, is also enriched in a suite of trace elements (Mo, Sb,

The coupled geochemistry of Au and As in pyrite from hydrothermal ore deposits

“…Similar to pyrite from Carlin-type deposits, growth zoning is a major factor controlling element distribution in pyrite in orogenic deposits. (Goldfarb et al, 2005;Large et al, 2007;Morey et al, 2008;Large et al, 2009;Sung et al, 2009;Thomas et al, 2011). The complexity of pyrite growth reflects the multistage evolution of orogenic Au deposits, where Au deposition is usually related to episodic pumping of fluids produced during greenschist to amphibolite facies devolatilization and that are structurally channelled into the retrograding parts of an orogen (Sibson et al, 1988;Goldfarb et al, 2005).…”

“…Gold and arsenic incorporation into pyrite is strongly coupled in pyrite from many different types of ore deposits, including Carlin-type Au (e.g., Cline, 2001;Emsbo et al, 2003;Reich et al, 2005;Muntean et al, 2011), porphyry Cu, Cu-Au, and epithermal Au (e.g., Cook and Chryssouliss, 1990;Deditius et al, 2008;Reich et al, 2013), orogenic Au (e.g., Morey et al, 2008;Large et al, 2007), volcanogenic massive sulphide (VHMS) (Huston et al, 1995;McClenaghan et al, 2004), iron-oxide Cu-Au (IOCG) (Foster et al, 2007) and…”

“…Reich et al (2005) showed that the maximum amount of Au that can be incorporated into pyrite is mainly a function of As concentration. In addition to As content, other factors that might control Au concentration in pyrite are the temperature of formation, subsequent metamorphism and/or alteration, the amounts of other trace elements, and the size of individual grains (e.g., Mumin et al, 1994;Fleet and Mumin, 1997;McClanaghan et al, 2004;Reich et al, 2005Large et al, 2007;Deditius et al, 2008, Deditius et al, 2011aMasslennikov et al, 2009). …”

Técnicas de caracterización mineral y su aplicación en exploración y explotación minera

“…Aplicaciones concretas al estudio de depósitos minerales se pueden encontrar en Watling et al (1995), Chenery et al, 1995, Wagner et al (2007, Large et al (2007), Hutchinson y McDonald (2008).…”

“…Los datos de LA-ICP-MS, junto con el estudio textural, indican que el oro es liberado progresivamente de los sulfuros masivos durante el metamorfismo y reprecipitado en venas. Por otra parte, Large et al (2007) han determinado, mediante LA-ICP-MS, en piritas sinsedimentarias (Sukhoi, Siberia) altos contenidos de "Au invisible" (hasta 12,2 ppm, con un valor promedio de 3.2 ppm) y de arséni-co (1900 ppm). Hutchinson y McDonald (2008) realizan un estudio detallado mediante LA-ICP-MS de los elementos del grupo del platino en sulfuros de la unidad Platreef (norte del complejo Bushveld).…”