Genesis of calcite vein in basalt and its effect on reservoir quality: A case study of the Carboniferous in the east slope of Mahu sag, Junggar Basin, NW China

XIA Lu,CAO Yingchang,BIAN Baoli,LIU Hailei,WANG Xiaoxue,ZHAO Yiwei,YAN Miaomiao

Fig. 6. Microscopic characteristics and filling periods of calcite veins in core sample from Well Ma 201. (a) 3877.13 m, calcite veins in basalt, plane-polarized light; (b) Horse-tooth shaped calcites with small crystal size are located in the lower margin of the vein with cleavage developed locally while the calcites with relatively larger crystal size and obvious cleavages are developed inside the vein, plane-polarized light; (c) Calcites in the lower margin of the vein show no cathodoluminescence whereas those inside the vein are maroon, cathodoluminescence; (d) (e) Chlorite can be discovered near the boundary between the two periods of calcites, plane-polarized light; (f) It is light blue fluorescence at the edge of the thick veins and tawny locally along the margin. Irregular veinlets show intermittent orange fluorescence, ultraviolet fluorescence; (g) Schematic distribution of three periods of calcite fillings.