Geochemical data generated by projects funded by the USGS Earth Mapping Resources Initiative (ver. 7.0, November 2022)

Sample Collection, Identification, and Submittal: Each Earth MRI affiliated agency was responsible for the collection of new samples, the acquisition of archived samples from State, industrial, or private collections, or the identification of samples stored in and pulled from the USGS National Geochemical Sample Archive. They were also responsible for providing sample collection, sample description, and sample location information in a specified spreadsheet format when submitting samples to the USGS for analysis. Once received by the USGS, submitted samples were logged into the Laboratory Information Management System (LIMS), prepared, and sent to the laboratories for analysis. The accompanying sample descriptive and location data were collated and stored in a digital database table.

Sample Preparation: Samples submitted to the USGS were prepared before sending them to the laboratories for analysis. Unless otherwise requested, samples were prepared using standard methodology. Rock samples were crushed and then a representative split of the material was ground in a shatterbox or ball mill using agate or aluminum corundum containers to -200 mesh (<75 microns) to ensure complete digestion of the sample when it was analyzed. Sediment samples were air-dried, sieved to a specified size fraction, and then ground in a vertical grinder with ceramic plates to -150 mesh (<100 microns). Soil samples were air-dried, disaggregated, sieved to a specified size fraction, and then ground in a vertical grinder with ceramic plates to -150 mesh. Previously-ground sample pulps pulled from the USGS National Geochemical Sample Archive were re-ground in a vertical grinder with ceramic plates to -150 mesh to ensure a uniform fineness of material.

Sample Analysis and Methods: Every sample submitted to AGAT Laboratories, LTD (AGAT) was analyzed, at a minimum, by a total digestion, 60- or 61-element method using inductively coupled plasma-optical emission spectrometry (ICP-OES) and inductively coupled plasma-mass spectrometry (ICP-MS). Most samples were also analyzed for major element oxides by wavelength dispersive x-ray fluorescence spectrometry (WDXRF) and a subset were analyzed by additional methods. Descriptions of the methods used (and their method codes) are as follows:

C_ICPOES_MS-60: Sixty or sixty-one elements (Al, Ca, Fe, K, Mg, P, S, Si, Ti, Ag, As, B, Ba, Be, Bi, Cd, Ce, Co, Cr, Cs, Cu, Dy, Er, Eu, Ga, Gd, Ge, Hf, Ho, In, La, Li, Lu, Mn, Mo, Nb, Nd, Ni, Pb, Pr, Rb, Re, Sb, Sc, Se, Sm, Sn, Sr, Ta, Tb, Te, Th, Tl, Tm, U, V, W, Y, Yb, Zn, Zr) are determined in rocks, minerals, sediments, and soils. Samples are fused at 750°C with sodium peroxide and the fusion cake dissolved in a dilute nitric acid. The resulting solution is analyzed by ICP-OES and ICP-MS. Data are deemed acceptable if recovery for all elements is ±15% at five times the Lower Detection Limit and the calculated Relative Standard Deviation (RSD) of duplicate samples is no greater than 15%.

C_WDXRF-MAJORS: Major elements are determined by WDXRF and reported as major element oxides (SiO2, TiO2, Al2O3, Fe2O3, MnO, MgO, CaO, Na2O, K2O, P2O5, BaO, Cr2O3, SrO, V2O5). The sample is fused with lithium metaborate/lithium tetraborate flux and the resultant glass disk is introduced into the WDXRF and irradiated by an x-ray tube. The method also provides a gravimetric loss on ignition (LOI). Data are deemed acceptable when recovery of each major oxide is ±5% at five times the Lower Detection Limit and the calculated percent Relative Standard Deviation (RSD) of duplicate samples is no greater than 5%.

C_FA_ICPMS-AU: Gold is determined by lead fusion and by ICP-OES and ICP-MS after collection by fire assay. The sample is mixed with fluxing agents to assist with melting and promote separation of waste (gangue) materials from the precious metals. After cooling, the gangue is separated and discarded as a glassy slag from the precious metal-containing lead button. This button is further heated on an absorbing magnesium oxide crucible to remove the lead and trace amounts of base metals. A small silver prill is left containing the precious metals. The silver prill is digested in aqua regia and then analyzed by ICP-OES and ICP-MS. Lower concentrations of Gold are measured by ICP-MS. Higher concentrations are measured by ICP-OES. Data are deemed acceptable when recovery of Gold is ±20% at five times the Lower Detection Limit and the calculated percent Relative Standard Deviation (RSD) of duplicate samples is no greater than 20%.

C_FA_AU-PD-PT: Gold, Palladium, and Platinum are determined by lead fusion and by ICP-OES and ICP-MS after collection by fire assay. The sample is mixed with fluxing agents to assist with melting and promote separation of waste (gangue) materials from the precious metals. After cooling, the gangue is separated and discarded as a glassy slag from the precious metal-containing lead button. This button is further heated on an absorbing magnesium oxide crucible to remove the lead and trace amounts of base metals. A small silver prill is left containing the precious metals. The silver prill is digested in aqua regia then analyzed by ICP-OES and ICP-MS. Data are deemed acceptable if recovery of Gold, Palladium, and Platinum is ±20% at five times the Lower Detection Limit and the calculated percent Relative Standard Deviation (RSD) of duplicate samples is no greater than 20%.

C_ISE-F: Fluoride is determined by ion-selective electrode (ISE) following a sodium hydroxide fusion. The sample is fused with a mixture of sodium hydroxide, potassium nitrate and silica to release fluoride ions from the sample matrix followed by dissolution of the fusion cake in dilute nitric acid. Prior to measuring the fluoride activity of the sample solution using an ion-selective electrode, an ammonium citrate solution is added to buffer the pH, maintain a constant ionic strength, and dissociate any metal ion-fluoride complexes. The fluoride concentration in the sample is then determined by interpolation from standard calibration curves. Data are deemed acceptable when recovery of Fluoride is ±20% at five times the Lower Detection Limit and the calculated percent Relative Standard Deviation (RSD) of duplicate samples is no greater than 20%.

C_TOTAL-S: Total Sulfur is determined in geologic materials by combustion followed by infrared detection on LECO instrumentation. A weighed sample is mixed with an accelerator and heated via an induction furnace to oxidize sulfur to sulfur dioxide. Moisture and dust are removed, and the sulfur dioxide gas is then measured by a solid-state infrared detector. Data are deemed acceptable when recovery of Total Sulfur is ±15% at five times the Lower Detection Limit and the calculated percent Relative Standard Deviation (RSD) of duplicate samples is no greater than 15%.

C_AQUA_REGIA: The sample is digested with aqua regia [nitric acid (HNO3) and hydrochloric acid (HCl)] and heated in a water bath for 1.5 hours at 85°C. The sample is then cooled to room temperature and analyzed by ICP-OES and ICP-MS for 51 elements (Al, Ca, Fe, K, Mg, Na, S, Ti, Ag, As, Au, B, Ba, Be, Bi, Cd, Ce, Co, Cr, Cs, Cu, Ga, Ge, Hf, Hg, In, La, Li, Mn, Mo, Nb, Ni, P, Pb, Rb, Re, Sb, Sc, Se, Sn, Sr, Ta, Te, Th, Tl, U, V, W, Y, Zn, Zr). Data are deemed acceptable when recovery for all 51 elements is ±15% at five times the Lower Detection Limit and the calculated Relative Standard Deviation (RSD) of duplicate samples is no greater than 15%.

Quality Assurance/Quality Control and Data Approval: AGAT Laboratories, LTD is accredited to ISO/IEC 17025:2005 and certified to the ISO 9001:2008 standard. The laboratory’s quality control protocol is to insert a reagent blank and a reference sample material sample with every batch of 20 samples to measure the analytical accuracy. Duplicate samples were analyzed at the end of the sample set to measure analytical variance as well as sample variance. Data passing the laboratory’s quality control criteria were sent to the USGS and then imported into the Laboratory Information Management System (LIMS).

All samples submitted to AGAT were accompanied with a set of USGS in-house geologic reference samples (GRMs) submitted blind to the laboratory at the rate of 10%. Using a program within the LIMS, a USGS Analytical Chemistry Quality Control Reviewer evaluated the data for the reference samples by comparing the “obtained” analytical value to the “expected” value for each element. The values must fall within the range of acceptance, which varies between ± 5% to ±20% depending on the analytical method. Analytical results for samples associated with the accepted quality control data were then released to the sample submitter and approved for release in this data product. Samples associated with rejected quality control data were re-analyzed by AGAT Laboratories until the resultant data were found to be “in control.” In addition to the GRMs, at least one randomly chosen sample per job was split and submitted blind to the laboratory as an analytical duplicate.

Preparation and Compilation of Data for Release: Analytical data results for samples submitted by Earth MRI collaborative projects, analyzed by USGS contract laboratories, and approved for release by a USGS Analytical Chemistry Quality Control Reviewer were pulled from the Laboratory Information Management System (LIMS). These records were merged with sample descriptive and location information previously provided by collaborative entities when the samples were submitted for analysis. Original latitude-longitude coordinates were converted, when necessary, to the WGS84 datum and then recorded in the Lat_WGS84 and Long_WGS84 fields. Sample preparation information obtained from sample submittal requests and Sample Control was consolidated and summarized in the Sample_Prep field. Analytical methods used on the samples were summarized by laboratory code in the Analytic_Mthds field. Samples of USGS geologic reference materials and analytical duplicates were identified in the QAQC_Sample field. Earth MRI projects and affiliated agencies were identified and recorded in the PID, Proj_Name, and Affiliation fields.

This initial version of the “Geochemical data generated by projects funded by the USGS Earth Mapping Resources Initiative” data release consists of 4,772 geochemical data records (including data for associated GRMs) that were approved for public release between April 14, 2020 and December 31, 2020.

Version 2.0 Update: Added 388 new geochemical records (Lab_ID's C-515082 through C-515157; C-515295 through C-515376; C-516824 through C-516913; C-517634 through C-517667; and C-517852 through C-517957) that were approved for public release between January 1, 2021 and March 31, 2021. Updated previously released records by adding results from new major element oxide analyses (C_WDXRF-MAJORS) to 1,132 records in 29 jobs (Job_IDs = MRP-18672, MRP-18673, MRP-18674, MRP-18675, MRP-18676, MRP-18677, MRP-18678, MRP-18679, MRP-18680, MRP-18685, MRP-18686, MRP-18687, MRP-18704, MRP-18718, MRP-18719, MRP-18720, MRP-18721, MRP-18722, MRP-18723, MRP-18724, MRP-18727, MRP-18728, MRP-18729, MRP-18730, MRP-18731, MRP-18732, MRP-18733, MRP-18734, MRP-18740). Laboratory corrections for major element oxide analyses (C_WDXRF-MAJORS) were received and updated for records with Job_ID = MRP-18769. Updated the QAQC_Values table with data for additional Geological Reference Materials. Version 2.0 of the CSV text file dataset and Microsoft Access database file now contains 5,160 records for Earth MRI-funded samples: 4,699 user-submitted sample or reference material records with coordinates plus 461 USGS GRMs without coordinates.

Version 3.0 Update: Added 323 new geochemical records from 11 new jobs (Job_ID's MRP-19076, MRP-19094 through MRP-19099, MRP-19106, MRP-19114, MRP-19127, and MRP-19128) that were approved for public release between April 1, 2021 and July 31, 2021. Updated the QAQC_Values table with data for additional Geological Reference Materials. Version 3.0 of the CSV text file dataset and Microsoft Access database file now contains 5,483 records for Earth MRI-funded samples: 4,994 user-submitted sample or reference material records with coordinates plus 489 USGS GRMs without coordinates.

Version 4.0 Update: Added 1,020 new geochemical records from 28 new jobs (Job_ID's MRP-18995 through MRP-18998, MRP-19130, MRP-19145, MRP-19152 through MRP-19155, MRP-19161, MRP-19166, MRP-19168 through MRP-19170, MRP-19180, MRP-19182, MRP-19183, MRP-19221, MRP-19222, MRP-19236, MRP-19256, MRP-19257, and MRP-19285 through MRP-19289) that were approved for public release between Aug 1, 2021 and October 31, 2021. Updated the QAQC_Values table with data for additional Geological Reference Materials. Version 4.0 of the CSV text file dataset and Microsoft Access database file now contains 6,503 records for Earth MRI-funded samples: 5,927 sample records with coordinates and 576 GRMs without coordinates.

Version 5.0 Update: Added 605 new geochemical records from 20 new jobs (Job_ID's MRP-19334, MRP-19342, MRP-19348 through MRP-19352, MRP-19360, MRP-19369, MRP-19370, MRP-19383 through MRP-19385, MRP-19445, MRP-19447, and MRP-19454 through MRP-19458) that were approved for public release between November 1, 2021 and February 28, 2022. Updated the QAQC_Values table with data for additional Geological Reference Materials. Version 5.0 of the CSV text file dataset and Microsoft Access database file now contains 7,108 records for Earth MRI-funded samples: 6,482 sample records with coordinates and 626 GRMs without coordinates.

Version 6.0 Update: Added 742 new geochemical records from 16 new jobs (Job_ID's MRP-19459 through MRP-19461, MRP-19463 through MRP-19474, and MRP-19545) that were approved for public release between March 1, 2022 and May 31, 2022. Updated the QAQC_Values table with data for additional Geological Reference Materials. Version 6.0 of the CSV text file dataset and Microsoft Access database file now contains 7,850 records for Earth MRI-funded samples: 7,162 sample records with coordinates and 688 GRMs without coordinates.

For data reported June 2022, the analytical laboratory changed the lower or upper detection limits for 10 elements analyzed by the C_AQUA_REGIA analytical method. The changed values are documented in two new fields (LowerDL2 and UpperDL2) in the Limits_AnalyticalMethods table.

Version 7.0 Update: Added 1,617 new geochemical records from 48 new jobs (Job_ID's MRP-19100 through MRP-19102, MRP-19294, MRP-19295, MRP-19306, MRP-19307, MRP-19347, MRP-19388, MRP-19449 through MRP-19453, MRP-19475, MRP-19511, MRP-19546 through MRP-19548, MRP-19550, MRP-19551, MRP-19559 through MRP-19564, MRP-19567, MRP-19568, MRP-19570 through MRP-19572, MRP-19586 through MRP-19589, MRP-19591 through MRP-19598, MRP-19646, MRP-19647, MRP-19652, and MRP-19653) that were approved for public release before August 31, 2022. Updated the QAQC_Values table with data for additional Geological Reference Materials. Version 7.0 of the CSV text file dataset and Microsoft Access database file now contains 9,467 records for Earth MRI-funded samples: 8,642 sample records with coordinates and 825 GRMs without coordinates.