Statement_of_Work_2.pdf

US Geological Survey Alaska Science Center Statement of Work

I. GENERAL INFORMATION

A. Introduction: The tasks for this contract are to provide 187Re/187Os analyses of sulfide minerals in mineralized rocks collected by geologists of the Geology Office of the Alaska Science Center of the USGS. Samples collected will include a range of lithologies and formation ages;

the results of the geochronologic analysis will be used in a variety of studies and will be made public. The primary responsibility of the task is to provide high quality analytical data for use in research studies. The staff of the performing laboratory is invited to participate in data interpretation, use, and publication of the data developed.

B. Background: Geochronologic studies are important tools in understanding the metallogenic history of Alaska and continually evolving technologies and requirement have precluded the development of geochronologic laboratories in the Alaska Science Center because of to the cost of staffing and equipment. No USGS laboratories with the necessary capabilities exist in the survey at this time, and this technique, which is the most robust direct‐dating technique for mineralization, must be completed at external labs. Nonetheless, the need for such analyses is critical to solving geologic research problems. Among the multiple analytical techniques available, 187Re/187Os analyses are the most robust direct‐dating technique of mineralization, with wide applicability to multiple system types in Alaska.

C. Definition/Applicable Documents: Applicable standards are well described in the scientific literature and we expect that any laboratory selected under this contract will follow those standards. See for example: Stein, H.J. (2014) Dating and Tracing the History of Ore Formation, in Holland, H.D. and Turekian, K.K. (editors) Treatise on Geochemistry, Second Edition, v. 13, p. 87‐118. Oxford: Elsevier; Selby, D., and Creaser, R.A., 2001, Re‐Os geochronology and systematics in molybdenite from the Endako porphyry molybdenum deposit, British Columbia, Canada: Economic Geology , v. 96, p. 197–204.; and Lawley, C.J.M., and Selby, D., 2012, Re‐Os geochronology of quartz‐enclosed ultrafine molybdenite:

Implications for ore geochronology: Economic Geology , v. 107, p. 1499–1505.

D. Scope: The samples submitted will address a variety of geologic issues. The contractor shall have a strong background in the application of 187Re/187Os in arsenopyrite, pyrite and molybdenite geochronology to geologic problems. Tasks include: sample evaluation for suitability to the problem at hand, sample preparation, analysis of appropriate phases, and full electronic reports of the resulting data and any appropriate interpretation of the analytical data. The requested work is for 52 analyses. Analyses will be a combination of direct dating molybdenite and developing isochrons to determine the age of multiple generations of arsenopyrite.

II. WORK REQUIREMENTS

A. Technical Requirements and Performance Metrics

The contractor shall operate a geochronologic laboratory known for high quality work and has practices that are uniform in sample handling, sample preparation, and mass spectroscopic analysis vital to the goals of the various studies for which samples will be submitted. The technical requirements below shall be evaluated for acceptance according to descriptions of laboratory protocols and methods on a laboratory website, in previously published reports or journal articles, or as part of a quote.

The time frame for completion of sample analysis will be not more than 30 days from the time of receipt.

Laboratory must demonstrate that they are open, able to conduct analyses and meet the required time frame for the completion of work at the time of award. During the COVID pandemic, some labs have been unable to remain open, or have uncertain plans of when analytical work will resume. Labs that have been closed may have backlogs. We require the lab to be able to receive, analyze, and produce results in the required turn‐ around time in order to advance our research objectives.

In concert with the project officer, sample analysis priority will be set on the basis of scientific need and laboratory protocol, to streamline acquisition of data.

Together with the project officer, mineral separations will be targeted by senior lab technicians with economic geology background, drawing on their skills as an economic geologist and Re‐Os expertise. The cost of preparation of mineral separates is included in the stated sum.

All samples will be analyzed with a mixed Re‐double Os spike following the specifications technique to correct for mass fractionation and determine any common Os. The double spike method is required for mass fractionation collection for Os and precisely determining common Os concentrations in the samples. The double spike will alleviate impossible age discrepancies between the age of the host rocks and mineralization contained within the host rocks.

Re and Os isotopic ratios will be measured on two state‐of‐the‐art Triton thermal ionization mass spectrometers dedicated to Re‐Os dating.

If a sample is not optimally spiked, the analysis will be redone at no additional cost, assuring that all delivered ages carry the highest precision possible.

Senior researcher / director should be an ore geologist with advanced degrees and with expertise in tearing apart the time‐space development of ore systems (preferably porphyry Cu, Mo, Au systems) with a strong background in geochronology, and specifically the integration of Re‐Os and UPb zircon techniques.

The lab should be US‐based.

Criteria for acceptance of Product or Service: Work will be considered acceptable if completed work meets institutional and professional standards for accuracy and precision. Work shall result in geologically reasonable dates with uncertainty of 0.5% or less for molybdenites. Samples with complications will be considered acceptable provided the report describes possible or probable causes of complexity. A publication ready Re‐Os data table will accompany the final report. Collaboration on publications is strongly encouraged to incorporate the expertise of the senior researcher and director of the lab.

B. Deliverable: A report delivered electronically to the Project Officer that contains age determination, analytical data, figures and tables for publication and written analytical interpretation of data for submitted samples.