Significance of Company and Internal Quality Assurance/ Quality Control (QAQC) XRF Results and Field Sample Reduction Procedures from the Macroasia Nickel Laterite Deposit, Brooke's Point, Palawan

by

Ramon A. L. Flores,

TMM Management Inc. Resource Development and Technical Services Manager
(ralflores@tmmphil.com)

Rikki Pamela L. Pineda,

Geologist, Macroasia Corporation
(rplpineda@gmail.com)

Rogel A. Santos,

TMM Management Inc. Site Manager, MAINEX Project
(rasantos@tmmphil.com)

Abstract

QAQC results are necessary to give a quantitative measure of accuracy and precision of any sampling programme, especially if it leads to high confidence in resource estimation which is the primary basis of establishing economic viability of mineral deposits.

The MacroAsia tenement enclosing 1,113.98 hectares is located at Brooke’s Point, Palawan. It consists of an Eocene-Oligocene ultramafic block belonging to the Palawan Ophiolite Complex mainly of harzburgite and some dunite thrusted against Creteceous-Eocene sediments with slivers of greenschists as a metamorphic sole. Exploration has been carried out since August 2006 in various phases.

For Phases 1 to  7 of the project, company checks were made for accuracy (grade- and matrix- matched internal standards every 20 samples) and precision (test pits and drillcore duplicates every 10 samples), mainly for geological and sampling error; and field crushed duplicates/ splits (Phase 7) to quantify field crusher and splitting errors were interpreted along with Intertek Testing Services (ITS) Laboratory (an ISO 17025 certified lab) QAQC samples.

The ITS QAQC samples consist of grade- and matrix-matched standards for accuracy (every 15 samples), second splits/ crushed duplicates from crushed rejects (every 15 from Phase 1 to 6; every 30 later in Phase 7); laboratory repeats (every 10 samples) from pulverized samples, which check for errors due to pulverizing and analysis; and blanks (for possible contamination). Sieve tests were also conducted every 10 samples to ensure at least 90% passing -200 mesh.

This paper mainly discusses the results for two elements of interest, Nickel and Iron.  Results show very good accuracy and minimal contamination over the entire programme, and larger errors attributable to natural geological variability and field sampling ((14% for nickel; 13% for iron) compared with combined errors due to crushing and splitting, pulverizing, and analysis (3% for nickel; 1.5% for iron). Elements/ Oxides with typical values near the detection limit expectedly give less precise results (e.g., Ca, Na, K, P2O5, TiO2, Co).

Field drying enabled crushing using a fabricated unit to reduce sample size to the manila lab by one-third, have at least one third increase in throughput, and reduction of manual labor by about half. Apart from reduction in noise and vibration from manual crushing, substantial savings of  over two-thirds of original cost were also achieved in transport and shipment from Palawan to ITS lab in Manila due to reduction in sample weight and volume. Drying time of the partially-dried samples in the field was also reduced in the Manila laboratory by half from the previous 16 hours per sample. Reporting turnaround also was cut down from the previous 2 weeks to just 1 week.

Continual monitoring of QAQC samples results in high confidence in assay results to be used for resource estimation, and formulation of enhanced procedures to minimize errors.