4.1 Weatherable minerals of post-tin mining areas
The number of weatherable minerals (including feldspar and ferromagnesian minerals) as native nutrient sources in post-tin mining areas is practically depleted, while the resistant minerals (eg. quartz, opaque and zircon) containing no essential crops are predominant. The number of quartz mineral is higher in soil tailings developing from sandstone (70-95%) than tailing from granite parent materials (48-73% quartz) (Table 1). The higher quartz mineral in sandstone materials is related to the nature of fluvial sediment containing higher sand fraction with high quartz composition (Ko, 1986). Other resistant minerals that bear no plant nutrients but occur in considerable amounts are opaque and zircon, further exacerbate nutrient problems. Given that tailing deriving from granite contains some K-bear minerals (orthoclase and sanidine), the K nutrient is slightly better compared to tailing derived from sandstone materials.
In the Dachang district, western China, the tin-cassiterite bearing mineral was formed in a granite-related magmatic-hydrothermal and the rock-forming minerals consisted of quartz (30-32%), K-feldspar (35-40%), plagioclase (20-25 %), biotite (3-6 %) and muscovite (1-2%) (Guo et al., 2018). In native soils (TBB4 and TBB5 profiles) of the present study, the turbid quartz was higher than transparent quarts, irrespective of parent material types, indicating transportation was a dominant process during soil formation. The higher transparent quartz than turbid quartz minerals in tailings suggests that the light sand fractions experienced less transportation. The exception was tailing TBB7 profile deriving from granite has higher turbid quartz than transparent quartz due to several times of re-mining (reworking practices at a tailing pile could mimic transportation processes).