Classification of Composite Pegmatite via Staining and Digital Image Processing in the Bulfat Complex, Qala Deza, NE (Iraq)

Abstract

The pegmatites associated classification aspects are usually considered with caution, due mainly to the relating coarse-grained texture enclosing interlocking grains often greater than 2.5 cm in size. In addition to the large size of the constituent mineral crystals, the Bulfat pegmatites clearly reflect a composite nature. Consequently, classifying these rocks by means of thin section and chemical classification processes turns out to be invalid. For such a seemingly insurmountable problem to be effectively surmounted, we consider implementing special classification criteria, which rests on a rather practical approach, whereby the Bulfat pegmatite peculiar mineralogy could be efficiently determined. Hence, for the mineral contents to be accurately quantified, the classification area must be noticeably greater than the thin section. Accordingly, the advanced calculation mode analysis has been implemented on two selected samples of polished slab area. The proposed computational process outcome appears to suggest that the slab area need be larger than 15 cm2, as a lower limit, for the pegmatite rocks’ classification procedure to be achieved. To overcome the difficulty associated with the studied samples relating coarse-grained sizes and chemical composites, we consider classifying the rocks in conformity with the classical classification schemes (i.e., by means of mineralogy content), using selective staining of K-feldspar and plagioclase on the examined rock slabs. Accordingly, the K-feldspar minerals are stained in yellow color by means of Sodium Cobaltinitrite (Na3 Co (NO2 )6), while the plagioclase feldspar is stained red by means of Amaranth (C20 H11 N2 Na3 O10 S3). The images concerning the polished rock slabs and the stained surfaces, as captured via a digital camera, have to be transformed into a different image mode using the ENVI software. An image processing analysis has been undertaken for the mineral proportions to be automatically evaluated and the appropriate nomenclature to be retrieved. Thus, the digital image processing is applied on polished slabs for the purpose of calculating and recalculating the color index M′, quartz, alkali-feldspar, and for the plagioclase proportions to be suitably plotted in a QAPF type of diagram. Moreover, and for the purpose of distinguishing between the Dioritic type of pegmatite and the Gabbroic pegmatite, the staining method, as associated with image processing technique, has been applied to the composite pegmatite rocks, while an aid extinction angle has been computed with regard to the plagioclase for the Plagioclase relating Anorthite content to be recognized. The image analyses as implemented on the stained polished slab of the Bulfat composite pegmatites appears to reveal well that the contrasting components’ contact with varying mineral constituents prove to mingle down to a small scale in single intrusion. Still, such finding appears to entail further dissection due mainly to the fact that the persistence of composite-pegmatite bodies with a small-scale contrasting composition might well have its explanation in the liquid associated immiscibility.