By Howard Yu
Porphyry copper deposits are an important resource for copper and other valuable metals or minerals. They are typically mined using large-scale, mechanized open-pit methods because of their large reserve, low grade, and shallow burial depth. Porphyry copper deposits are a type of hydrothermal deposit. Characteristics of porphyry copper deposits include:
- Their mineralization is temporally and spatially related to neutral-to-acidic porphyry bodies.
- Their formation is somewhat intrinsically related to volcanic-intrusive activities.
- They are characterized by certain alteration and mineralization zonation.
- Their ore is in disseminated veins.
As contemporaneous and post-period products of porphyry copper ore formation, clay minerals are important guides to discover, explore, and extract copper ore deposits.
Testing the Clay Minerals with Handheld XRF
The XRF test was conducted using the Vanta™ C Series analyzer (VCA model) equipped with a silver (Ag) target X-ray tube. Designed to operate in harsh field conditions, the rugged analyzer is IP55 rated and is built to pass the drop test required by the US Department of Defense standard (MIL-STD-810G). The built-in silicon drift detector (SDD) combined with Olympus’ proprietary Axon Technology™ enables ultra-high-speed detection and lower limits of detection (LODs).
Another advantage of using the Vanta analyzer is that the sample can be analyzed immediately without any special processing. In fact, qualitative and quantitative information about the sample’s elemental composition can be obtained within 20 seconds.
Testing the Clay Minerals with Portable XRD Analysis
The XRD test was performed using the TERRA™ II portable XRD analyzer equipped with a cobalt (Co) target X-ray tube. The analyzer’s XRD testing capabilities combine proprietary technologies from both Olympus and the National Aeronautics and Space Administration (NASA).
The TERRA II analyzer features a unique sample loading system. It requires only about 15 mg of 100-mesh-sieve (<150 μm) powdered sample to collect both structural (mineralogical/crystallographic) information and approximate elemental (chemical) information in less than 10 minutes.
- The amounts of clay minerals (mainly illite and montmorillonite) in the three samples increased from low clay to high clay.
- The amounts of quartz, alunite, and pyrite decreased from low clay to high clay.
Portable X-Ray Analysis Methods for Testing Clay Minerals
The discovery of pyrophyllite formed by special alteration is also important for exploring and extracting porphyry copper ores. The elemental data (e.g., Ca, Fe, etc.) from the XRF analyzer and the mineral composition data from the XRD analyzer could corroborate each other, helping to confirm accurate analysis results on this batch of samples.
Learn more: https://www.olympus-ims.com/en/insight/porphyry-copper-deposits-clues/
