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Geochemistry / Assay

Which Geochemical Digestion, Fusion or Instrumental Method Do I Need?

  1. Fire Assay - Samples are mixed with a flux which contains litharge (PbO) and a collector (Ag) and fired at 1150 degrees C. A resultant lead button is cupelled to form a Ag bead which is dissolved and Au (Code 1A2) or Au, Pt, Pd (code 1C/OES-ICP, 1Cexp2, or 1Cresearch(ICP/MS) can be determined. For the full platinum group elements (PGE) a nickel sulphide fire assay dissolution process is used (code 1B2). 

  2. Aqua Regia digestion -This partial digestion uses a mixture of hydrochloric and nitric acids to dissolve sulphides, some oxides and some altered silicates. Generally base metals will be totally dissolved but this depends on mineralogy (not silicate Ni or Zn in gahnite). Multielement geochemical packages such as Code 1E, 1E1, 1E2, and1E3 group are analyzed by ICP and Ultratrace 1 (ICP/MS) or Ultratrace 2(ICP/MS+ICP/OES). This digestion can be combined with other methods like INAA to give Code 1EPIand code1EPI/MS.

  3. "Near Total" Digestion - This digestion is as total as an acid digestion can get but will still not dissolve very resistate phases like chromite, barite, monazite, sphene, xenotime, etc. The digestion uses nitric, perchloric, hydrofluoric and hydrochloric acids with temperatures to 260 degrees C. The method is NOT suitable for rare earth elements. This digestion is used for the 1F group of packages by ICP/OES or the Ultratrace 4 package. The digestion is also combined with instrumental methods to give code 1H (INAA+ICP/OES), code 1H2 and Ultratrace 3 (INAA+ICP/OES+ ICP/MS), Ultratrace 5 (INAA+ICP/MS) or Ultratrace 6 (ICP/OES+ICP/MS). 

  4. Sodium Peroxide Fusion - This fusion process will result in total metals. This method is not suitable if sodium is required. A multielement package, Ultratrace 7 combines ICP/OES with ICP/MS.

  5. Lithium Metaborate/tetraborate Fusion - This fusion process will result in total metals and is ideal for lithogeochemistry including major oxides and trace elements including REE and other high field strength elements. The group 4B (ICP/OES), 4B2 std (ICP/MS), 4B2 research (ICP/MS), 4 Litho (ICP/OES+ICP/MS), 4 Lithoresearch (ICP/OES+ICP/MS) provide both assay quality but at major levels as well as geochem trace levels. Code 4C and 4C Laterite combine major oxides with some minor elements using the fusion glass disk XRF methods. 

  6. Instrumental Methods 1) Pressed pellet XRF- Samples are compressed into a pellet and analyzed instrumentally. Only lower levels of metals can be done accurately by this method. Codes 4C1 or 4E-XRF provides suites of trace levels. 2) Combustion (LECO, Eltra-CHNS) can be analyzed directly without pretreatment by placing in a special furnace linked to infrared detectors. Code 4F-C,S,N or the Code 5G carbon sulphur speciation package is done by this method. 3)CO2 and H2O+/- is determined instrumentally using an Eltra analyzer.

  7. INAA - Instrumental Neutron Activation Analysis- Samples are encapsulated and irradiated in a nuclear reactor. After a suitable decay samples are measured for their emitted gamma ray fingerprint. INAA is very good for Au, Co, As, Sb, W, Ta, U, Th, Cs, In, Re, Cl and lower levels of REE. Codes 1D, 1D enhanced, 2A (humus), 2B (vegetation), 3A (heavy minerals), 4A expl, 4A research, 5A, 5B, 5S make use of INAA to provide multielement packages. A special variation of reactor based method called delayed neutron counting (DNC) is used for uranium assay or geochem. Boron is also determined by a special type of reactor based method called prompt gamma analysis. INAA when combined with Nickel sulphide fire assay is used for the platinum group metal assay (code 1B1, 1B2).

Activation Laboratories Ltd. | 41 Bittern Street, Ancaster, Ontario, L9G 4V5, Canada | TF: +1.888.228.5227
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