The origin and composition of carbonatite-derived carbonate-bearing fluorapatite deposits

Carbonate-bearing fluorapatite rocks occur at over 30 globally distributed carbonatite complexes and represent a substantial potential supply of phosphorus for the fertiliser industry. However, the process(es) involved in forming carbonate-bearing fluorapatite at some carbonatites remain equivocal, with both hydrothermal and weathering mechanisms inferred. In this contribution, we compare the paragenesis and trace element contents of carbonate-bearing fluorapatite rocks from the Kovdor, Sokli, Bukusu, Catalão I and Glenover carbonatites in order to further understand their origin, as well as to comment upon the concentration of elements that may be deleterious to fertiliser production. The paragenesis of apatite from each deposit is broadly equivalent, comprising residual magmatic grains overgrown by several different stages of carbonate-bearing fluorapatite. The first forms epitactic overgrowths on residual magmatic grains, followed by the formation of massive apatite which, in turn, is cross-cut by late euhedral and colloform apatite generations. Compositionally, the paragenetic sequence corresponds to a substantial decrease in the concentration of rare earth elements (REE), Sr, Na and Th, with an increase in U and Cd. The carbonate-bearing fluorapatite exhibits a negative Ce anomaly, attributed to oxic conditions in a surficial environment and, in combination with the textural and compositional commonality, supports a weathering origin for these rocks. Carbonate-bearing fluorapatite has Th contents which are several orders of magnitude lower than magmatic apatite grains, potentially making such apatite a more environmentally attractive feedstock for the fertiliser industry. Uranium and cadmium contents are higher in carbonate-bearing fluorapatite than magmatic carbonatite apatite, but are much lower than most marine phosphorites

Postprandial zinc stable isotope response in human blood serum

In recent years, considerable advances have been made in the field of medical isotope metallomics, but numerous fundamental physiological processes remain to be investigated. Past studies report that blood serum...</p

Zinc stable isotope analysis reveals Zn dyshomeostasis in benign tumours, breast cancer, and adjacent histologically normal tissue

The disruption of Zn homeostasis has been linked with breast cancer development and progression. To enhance our understanding of changes in Zn homeostasis both inside and around the tumour microenvironment, Zn concentrations and isotopic compositions (δ66Zn) were determined in benign (BT) and malignant (MT) tumours, healthy tissue from reduction mammoplasty (HT), and histologically normal tissue adjacent to benign (NAT(BT)) and malignant tumours (NAT(MT)). Mean Zn concentrations in NAT(BT) are 5.5 µg g−1 greater than in NAT(MT) (p = 0.00056) and 5.1 µg g−1 greater than in HT (p = 0.0026). Zinc concentrations in MT are 12.9 µg g−1 greater than in HT (p = 0.00012) and 13.3 µg g−1 greater than in NAT(MT) (p < 0.0001), whereas δ66Zn is 0.17‰ lower in MT than HT (p = 0.017). Benign tumour Zn concentrations are also elevated compared to HT (p = 0.00013), but are not significantly elevated compared to NAT(BT) (p = 0.32). The δ66Zn of BT is 0.15‰ lower than in NAT(BT) (p = 0.045). The similar light δ66Zn of BT and MT compared to HT and NAT may be related to the isotopic compensation of increased metallothionein (64Zn-rich) expression by activated matrix metalloproteinase (66Zn-rich) in MT, and indicates a resultant 66Zn-rich reservoir may exist in patients with breast tumours. Zinc isotopic compositions thus show promise as a potential diagnostic tool for the detection of breast tumours. The revealed differences of Zn accumulation in healthy and tumour-adjacent tissues require additional investigation