X-RAY DIFRACTOMETRY MINERALOGY OF GOLD MINERALS AND PLATINUM IN COLOMBIA

The x-ray difractometry technics is used in Laboratorio Nacional de Suelos (IGAC,COL) in the analysis of clay and powder fraction (clay-small size sand) since 40 years ago, the theory used is dued by Thorez and some other authors of clay difractometry.

The Middle Magdalena Valley Basin is the mean and more known Oil Basin in Colombia. is a foreland basin between two ridges (eastern and central ridge whose elevations are over 4000 and 5000 meters over sea level), the building of the ridges are dued by a chrystalline basement in augen-gneiss, muscovite-cordierite schist and chlorite metapellites precambian age, over them an erosive deposition of mesozoic shales and sandstones alternancy of 8 kilometers in extention; tertiary and quaternary sedimentary prism are almost 10 Km in thickness. The age of uplift of the ridge is eocene andine orogeny, the mechanism is astenospheric domming in the Guyana Craton NW border.

In a former fieldtrip the author caracterized the oil productive basin of Middle Magdalena Basin, in Bolivar State, Cantagallo Town, recently destroyed by floods in Magdalena river basin. The camp in a known oil reservoir since the 1920´s decade by Texas Oil Co. An study on the soil sand horizon composition shown an important presence in gold mineral (Sylvanite, an AuAgTe4 mineral probably oxidized) and Platinum, in a mixture with Quartz and K-Ba Rich Muscovite. Those minerals where evaluated in powder in the d X-Ray difractometer.

In the evaluation of the material the metallic brigthness were the most important clue for identification.

In the X-Ray Diphractometry analysis the material were compared with other minerals pattern like mica, oxides, carbonates and some other, but the dimensions of the chrystalline cell match with platinum pattern and sylvanite one time the quartz signal were eliminated in the background filter and the mean mica K-Ba Muscovite were identified.

The dimensions measured of the chrystaline shell of Platinum, Pt in A (Armstrongs) are 2.28034 A; 1.97123 A; 1.39476 A (until 1.37113 A).