Numerous world class mineral deposits make the Kola Peninsula a ‘Mecca’ for mineralogists, and key economic deposits make it one of Russia's most important industrial areas. For geologists there is the challenge of explaining how this situation has come about.
The Tundulu and Kangankunde carbonatite complexes in the Chilwa Alkaline Province, Malawi, contain late-stage, apatite-rich lithologies termed quartz-apatite rocks. Apatite in these rocks can reach up to 90 modal% and displays a distinctive texture of turbid cores and euhedral rims. Previous studies of the paragenesis and rare earth element (REE) content of the apatite suggest that heavy REE (HREE)-enrichment occurred during the late-stages of crystallization. This is a highly unusual occurrence in intrusions that are otherwise light REE (LREE) enriched. In this contribution, the paragenesis and formation of the quartz-apatite rocks from each intrusion is investigated and re-evaluated, supported by new electron microprobe (EPMA) and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) data to better understand the mechanism of HREE enrichment. In contrast to the previous work at Tundulu, we recognize three separate stages of apatite formation, comprising an "original" euhedral apatite, "turbid" apatite, and "overgrowths" of euhedral late apatite. The crystallization of synchysite-(Ce) is interpreted to have occurred subsequent to all phases of apatite crystallization. The REE concentrations and distributions in the different minerals vary, but generally higher REE contents are found in later-stage apatite generations. These generations are also more LREE-enriched, relative to apatite that formed earlier. A similar pattern of increasing LREE-enrichment and increased REE concentrations toward later stages of the paragenetic sequence is observed at Kangankunde, where two generations of apatite are observed, the second showing higher REE concentrations, and relatively higher LREE contents.
Research Article| October 01, 2010 Aragonite in olivine from Calatrava, Spain—Evidence for mantle carbonatite melts from >100 km depth Emma R. Humphreys; Emma R. Humphreys 1Department of Earth Sciences, University of Bristol, Wills Memorial Building, Bristol BS8 1RJ, UK2Department of Mineralogy, Natural History Museum, Cromwell Road, London SW7 5BD, UK Search for other works by this author on: GSW Google Scholar Ken Bailey; Ken Bailey 1Department of Earth Sciences, University of Bristol, Wills Memorial Building, Bristol BS8 1RJ, UK Search for other works by this author on: GSW Google Scholar Chris J. Hawkesworth; Chris J. Hawkesworth 1Department of Earth Sciences, University of Bristol, Wills Memorial Building, Bristol BS8 1RJ, UK3University of St Andrews, College Gate, North Street, St Andrews, Fife KY16 9AJ, UK Search for other works by this author on: GSW Google Scholar Frances Wall; Frances Wall 2Department of Mineralogy, Natural History Museum, Cromwell Road, London SW7 5BD, UK4Camborne School of Mines, University of Exeter, Cornwall Campus, Penryn, Cornwall TR10 9EZ, UK Search for other works by this author on: GSW Google Scholar Jens Najorka; Jens Najorka 2Department of Mineralogy, Natural History Museum, Cromwell Road, London SW7 5BD, UK Search for other works by this author on: GSW Google Scholar Andrew H. Rankin Andrew H. Rankin 5School of Geography, Geology and the Environment, Kingston University, Surrey KT1 2EE, UK Search for other works by this author on: GSW Google Scholar Geology (2010) 38 (10): 911–914. https://doi.org/10.1130/G31199.1 Article history received: 09 Mar 2010 rev-recd: 07 May 2010 accepted: 20 May 2010 first online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Emma R. Humphreys, Ken Bailey, Chris J. Hawkesworth, Frances Wall, Jens Najorka, Andrew H. Rankin; Aragonite in olivine from Calatrava, Spain—Evidence for mantle carbonatite melts from >100 km depth. Geology 2010;; 38 (10): 911–914. doi: https://doi.org/10.1130/G31199.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Aragonite, as an inclusion in olivine from a leucitite lava flow, provides evidence for high-pressure crystallization and carbonatitic activity beneath the geophysical lithosphere in Calatrava, Spain. The aragonite occurs as a single crystal within olivine (Fo87), interpreted to have crystallized from a carbonated silicate melt at mantle depths. Experimental data constrain the stability of aragonite to depths of >100 km at CO2-H2O-bearing mantle solidus temperatures. This is the first documented evidence of magmatic aragonite crystallized in the mantle. Entrained as xenocrysts, the olivines have not crystallized from the carrier melts, which must have formed deeper within the mantle. Lead isotope data of the leucitite and carbonate inclusions indicate that the source melts show isotopic enrichment relative to mid-oceanic ridge basalt and most ocean island basalt. Our evidence strengthens the argument for direct and deep mantle-derived volcanic carbonatite in alkaline volcanic provinces containing maar-type volcanism, such as Calatrava. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
Various rare earth elements minerals occur in late‐stage carbonatites within the Kola Alkaline Province. The carbonatites are mineralogically diverse rocks and contain calcite, dolomite, magnesite, siderite and rhodochrosite as rock‐forming minerals. REE‐ minerals are present as accessory, minor and rock‐forming minerals related to two distinct mineral assemblages: primary (magmatic or crystallized from carbohydrothermal solution – e.g. burbankite) and secondary (metasomatic – e.g. ancylite). The REE‐minerals tend to be enriched in light REE, with the Y‐rich mckelveyite‐ group minerals as rare exceptions. Stable and radiogenic isotopes indicate a deep mantle source for C, O, Sr and Nd in primary minerals and it is thought that the original formation of REE rich carbonatites was a result of multi‐stage fractional crystallization of silicate‐carbonate melts.
Abstract A detailed study of weathered pyrochlore in the laterite above carbonatite at Lueshe, NE Zaire, has been made in order to determine its chemical and textural variations. Pyrochlore in fresh carbonatite at Lueshe is close to an ideal formula of (Ca,Na) 2 Nb 2 O 6 (OH,F) (where a general formula is A 2−x B 2 O 6 (OH,F) 1−y ·zH 2 O. The first and principal change on weathering occurs at the base of the profile and involves the leaching and partial exchange of A cations together with hydration. This change appears common to weathered pyrochlore worldwide. As a result weathered pyrochlore at Lueshe has a large apparent A cation deficiency with A totals between 0.25 and 0.59. The B cations remain stable. Abundant kalipyrochlore is unique to Lueshe and is thought to be related to the abundance of potassium feldspar in the fresh carbonatite, showing that the actual composition of weathered pyrochlore is a characteristic of a particular deposit. Weathered profiles at Lueshe are not simple trends from the least to most leached compositions. Further factors including variation in whole rock mineralogy and chemistry, and cation exchange and uptake are responsible for local concentrations of strontio-, bario- and calcium-rich, sodium-poor pyrochlore in the ore body, as well as rims of ceriopyrochlore on kalipyrochlore. The most important textural relationship in the Lueshe pyrochlore is the intimate intergrowth with crandallite in the most weathered parts of the laterite. Although pyrochlore persists throughout the weathering profile, niobium-beating goethite is thought to represent the final product of pyrochlore breakdown.
Rare earth elements (REE) are considered as critical metals for electronics and green technology. The REE fluorcarbonates are one of the main REE ore minerals, common in many different types of REE deposit and yet some of their fundamental properties have still not been determined. This study measured the magnetic properties of pure REE fluorcarbonate single crystal minerals using a vibrating sample magnetometer (VSM) and determined their elemental compositions using electron probe microanalysis (EPMA). The results provide the first measurements of the magnetic behaviour and susceptibility of REE fluorcarbonates other than bastnäsite-(Ce). The magnetic susceptibility of REE fluorcarbonates varies systematically from one mineral to another and is highly dependent on the mineral chemistry. It is positive (paramagnetic) for bastnäsite-(Ce) and gradually decreases as the amount of Ca increases in parisite-(Ce), becoming negative (diamagnetic) for the Ca-rich member of the series, röntgenite. Synchysite-(Ce) is difficult to measure, generate good signal and acquire accurate readings because it practically always occurs as <5 mg crystals. Its magnetic susceptibility in samples from a REE ore deposit was experimentally determined by magnetic separation and checked by an associated study using a SQUID magnetometer, synchysite-(Ce) behaved as a diamagnetic mineral. This can be explained by the increase of Ca content and decrease of REE content, in addition to the variations in the layered structure common to the REE fluorcarbonate series minerals. Given the wide range of magnetic susceptibility of REE fluorcarbonates, it is important that the mineralogy is determined carefully before setting up a mineral processing flow sheet.
Diamonds – rough stones, cut stones, host rocks, historical jewellery, contemporary jewellery, and hi‐tech materials – were the stars of an exhibition at the Natural History Museum in London in 2005, the biggest of its kind the Museum had ever staged. Why diamonds are so rare, how they have been valued through history, and the links between the unique properties of diamond and its use were the key themes of the exhibition.
'%3e%3cpath fill='%23012169' d='M0 0v30h60V0z'/%3e%3cpath stroke='%23fff' stroke-width='6' d='m0 0 60 30m0-30L0 30'/%3e%3cpath stroke='%23C8102E' stroke-width='4' d='m0 0 60 30m0-30L0 30' clip-path='url(%23b)'/%3e%3cpath stroke='%23fff' stroke-width='10' d='M30 0v30M0 15h60'/%3e%3cpath stroke='%23C8102E' stroke-width='6' d='M30 0v30M0 15h60'/%3e%3c/g%3e%3c/svg%3e)
'/%3e%3cuse xlink:href='%23a' transform='rotate(23.036 .093 25.536)'/%3e%3cuse xlink:href='%23a' transform='rotate(45.87 1.273 16.18)'/%3e%3cuse xlink:href='%23a' transform='rotate(69.945 .996 12.078)'/%3e%3cuse xlink:href='%23a' transform='rotate(20.66 -19.689 31.932)'/%3e%3c/svg%3e)
