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,
[1] In this study we used LA-ICP-MS (laser ablation-inductively coupled plasma-mass spectrometry) to determine U-Pb ages of 5 zircon samples of known age ($1800 Ma to $50 Ma) in order to determine the reproducibility, precision, and accuracy of this geochronologic technique. This work was performed using a ThermoFinnigan Element2 magnetic sector double-focusing ICP-MS coupled with a New Wave Research UP-213 laser system. The laser ablation pit sizes ranged from 30 to 40 mm in diameter. Laserinduced time-dependent fractionation is corrected by normalizing measured ratios in both standards and samples to the beginning of the analysis using the intercept method. Static fractionation, including those caused during laser ablation and due to instrumental discrimination, is corrected using external zircon standards. Total uncertainty for each laser analysis of an unknown is combined quadratically from the uncertainty in the measured isotope ratios of the unknown and the uncertainty in the fractionation factors calculated from the measurement of standards. For individual analyses we estimate that the accuracy and precision are better than 4% at the 2 sigma level, with the largest contribution in uncertainty from the measurement of the standards. Accuracy of age determinations in this study is on the order of 1% on the basis of comparing the weighted average of the LA-ICP-MS determinations to the TIMS ages. Due to unresolved contributions to uncertainty from the lack of a common Pb correction and from potential matrix effects between standards and unknowns, however, this estimate cannot be universally applied to all unknowns. Nevertheless, the results of this study provide an example of the type of precision and accuracy that may be possible with this technique under ideal conditions. In summary, the laser ablation technique, using a magnetic sector ICP-MS, can be used for the U-Pb dating of zircons with a wide range of ages and is a useful complement to the established TIMS and SHRIMP techniques. This technique is especially well suited to reconnaissance geochronologic and detrital zircon studies.
We are grateful to Mr. Bryan Yap, President of Lepanto Consolidated Mining Company, for permission to conduct this study in the Mankayan district, for providing access to the air magnetic and radiometric survey results, and for permission to publish the outcome of this study. This work is part of AMIRA Project P765, completed in December, 2006, at CODES, University of Tasmania. The project was sponsored by Anglo American, Anglo Gold Ashanti, Gold Fields, Newcrest, Newmont, Placer Dome, and Teck Cominco, as well as Barrick in the final year, with additional funding provided by the Australian Research Council. We acknowledge the discussion and ideas provided by representatives of the sponsoring companies, and assistance by the AMIRA research coordinator Alan Goode. We thank Lyndon Bradish and Froilan Conde, plus many other Lepanto staff, including Bene, Danny, Ed, Louie, Perfecto, Perry, Ric, and Willy, for their assistance, and Dave Braxton for help in the field. Paddy Waters of Anglo American Philippines generously provided logistic support and funding for some of the whole-rock geochemical analyses. We appreciate the help from CODES staff, including Simon Stephens for sample preparation, Sarah Gilbert and Leonid Danyushevsky for LA-ICP-MS analyses, and June Pongratz for report preparation. We thank Roger Stoffregen for comments on an early version of the manuscript, and John Thompson and Raymond Jannas for useful reviews.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.