The occurrence and genesis of the phosphatic nodules in the Lower Triassic quartzites of the Male Karpaty Mts. (Central Western Carpathians)

Small dark grey phosphorus-rich concretions, or locally also the relics of stratiform bodies (up to 12 cm thick), were identified in the Male Karpaty Mts. (Tatric unit of the Western Carpathians, SW Slovakia) within the cover basal quartzites. The dark brown phosphate cement, of presumably biogenic (planctonic) origin, is composed of the cryptocrystalline to fine-grained aggregate of fluorapatite, which fills the space between the quartz clasts. The apatite content in studied rock reaches ca 10-12 vol. %, and in the flat black nodules even more. Development of tiny apatite crystals, as well as the Sr-enriched phases (up to 4.6 wt.% SrO) were probably related to diagenetic or anchimetamorphic processes. In comparison to the common quartzites, as well as to surrounding crystalline rocks, apatite-bearing quartzite shows a noticeable increase in the content of P, Ca, F, Sr, As, U, MREE and partly HREE. Origin of the phosphate concretions may be related to the local marine impact in the overall continental sedimentation environment of the Lower Triassic quartzites. A discussion raises a question of possible syn-sedimentary genesis of a special type of tourmaline pebbles, occurring in the same rock-unit from nearby locality. (authors)