• The Airless Project

      Allington-Jones, L; Trafford, A (Natural Sciences Collections Association, 2017-04-20)
      A project to combat pyrite oxidation at the NHM (London, UK) is currently in its second year. The project aims to undertake conservation treatments and store highest risk specimens in low oxygen microenvironments. An emergent benefit of the conservation-driven project has been the digitisation of specimens on the collection management system KE Emu, through the use of barcodes and web-based applications.
    • Alkali-rich replacement zones in evolved NYF pegmatites: metasomatic fluids or immiscible melts?

      Muller, A; Spratt, J; Thomas, R; Williamson, BJ; Seltmann, Reimar (International Mineralogical Association, 2018-08-13)
      IMA2018 Abstract submission Pegmatite mineralogy, geochemistry, classification and origins IMA2018-1337 Alkali-rich replacement zones in evolved NYF pegmatites: metasomatic fluids or immiscible melts? Axel Muller* 1, John Spratt2, Rainer Thomas3, Ben J. Williamson4, Reimar Seltmann2 1Natural History Museum, University of Oslo, Oslo, Norway, 2Department of Earth Sciences, Natural History Museum, London, United Kingdom, 3Chemistry and Physics of Earth Materials, German Research Centre for Geoscience GFZ, Potsdam, Germany, 4Camborne School of Mines, University of Exeter, Penryn, United Kingdom What is your preferred presentation method?: Oral or poster presentation : Replacement zones (RZ), which are a common feature of evolved granitic pegmatites, are irregular, commonly alkali-rich zones superimposing, cross-cutting and replacing the primary zonation in almost all consolidated pegmatite bodies. RZ are widely considered to result from late-stage metasomatism even though little is known about the melts and/or fluids involved in their formation. However, the observed textures and mineral paragenesis of RZ cannot be explained by metasomatism in a strict sense. In this study, the nature of the late stage silicate melt forming “cleavelandite” RZ is assessed from textural, mineralogical, chemical and melt inclusion studies of evolved, Proterozoic Niobium-Yttrium-Fluorine (NYF) rare metal pegmatites from Evje–Iveland, southern Norway. These were studied as they are mineralogically simple, compared with RZ in evolved Lithium-Caesium-Tantalum (LCT) pegmatites. Silicate melt inclusions in RZ-forming topaz and “cleavelandite” document high H2O contents of up to18 wt.% of the F-rich silicate melt from which the RZ crystallized. In addition, from mineral compositions (“cleavelandite”, “amazonite”, white mica, garnet, columbite group minerals, topaz, fluorite, and beryl), they must have also been strongly alkaline (Na-dominated) with enrichments in F (at least 4 wt.%), Cs, Rb, Ta, Nb, Mn, Ge, Bi, As, and in some cases also Li compared with host pegmatites. These elements are concentrated in a few RZ-forming minerals resulting in very distinctive mineral-trace element signatures. “Amazonite” is strongly enriched in Cs and Rb and often white mica and beryl in Li and Cs. To acquire these mineral compositions, the overall Li-Cs-Ta-poor Evje-Iveland original pegmatite melt must have undergone extreme internal chemical differentiation resulting in melt/melt immiscibility aiding rheology contrasts and resulting in RZ formation. The resulting RZ-forming H2O-F-rich silicate melt would have shown large differences in viscosity and density, and therefore physical flow/transport properties, to the host pegmatite melt resulting in discordant contacts. The mineralogy and melt inclusion data from the Evje-Iveland pegmatites document a gradient of crystallization temperatures within the investigated pegmatite bodies with highest temperatures at the pegmatite margin (during initial emplacement, ~680°C) and lowest temperatures within the RZ (<500°C). Considering the temperature and pressure conditions of the host rocks gneisses and amphibolites (~650°C, up to 5 kbar) at the time of pegmatite emplacement and the crystallization conditions of the RZ, the Evje- Iveland pegmatites and RZ likely formed over a period of 2.2 million years, assuming an exhumation rate of 1.5 mm per million years and a geothermal gradient of 45°C km-1. Such a long crystallization time contradicts the classical view that pegmatites represent strongly undercooled melts which crystallize relatively fast.
    • Blue Whale on the Move: Dismantling a 125 Year-Old Specimen

      Bernucci, A; Cornish, L; Lynn, C (museum fur naturkunde berlinBerlin, Germany, 2016)
      The Natural History Museum (London, UK) intends to suspend a 25 metre-long, blue whale (Balaenoptera musculus) from its central Hintze Hall. Alongside other specimens which are to be put on open display in this space the environment was looked at in terms of sustainable improvements. Works are being undertaken to improve the conditions by utilizing natural ventilation and re-using existing duct work. This specimen, acquired by the Museum in 1891, was suspended from the ceiling of the Mammal Hall, where it has been on display since 1934. Conservators worked with a specialist specimen handling company to carefully dismantle and remove each of the 220 bones from its original mount. The skull required a special frame and a precise calculation of movement to dismantle it and remove it. Many complex decisions were made during this process – as each bone removal did not dictate what the next would bring. During the dismantling phase, the conservation team have had to address the many requirements of curators, researchers, senior management and the media.
    • Classification and characterisation of magmatic-hydrothermal tourmaline by combining field observations and microanalytical techniques

      Drivenes, K; Brownscombe, W; Larsen, RB; Seltmann, Reimar; Spratt, J; Sørensen, BE (IOP Publishing, 2020)
      Tourmaline from the St. Byron lobe of the Land’s End granite, SW England, was assessed by macroscopic, optical and quantitative microanalytical methods. In total, seven types of tourmaline were distinguished. The seven types reflect different crystallisation environments and stages in the magmatic-hydrothermal transition. Types 1-3 are interpreted to represent a gradual transition from tourmaline crystallising from a silicate melt to precipitation from magmatic aqueous fluids. Types 5-7 crystallised at subsolidus conditions from a different fluid generation than types 1-3. These fluids may be magmatic or mixed with other fluids (e.g., meteoric or formation waters). The Sn-mineralisation in the area is mostly related to the latter fluid generation, and the mineralising potential is reflected by the tourmaline composition.
    • Conservation in a Barcode Age: A cross-discipline re-storage project for pyritic specimens

      Allington-Jones, L; Trafford, A (International Council of Museums, 2017-01-01)
      The dichotomy of conservation and access has long been recognised within the museum profession. The recent push for digitisation has added a new dimension to this argument: digital records can both increase potential access, due to increased awareness of the existence of objects, and decrease potential handling, since a more thorough awareness of an object creates a more informed decision regarding whether access is actually necessary. The use of barcodes and the creation of digital resources have therefore been incorporated into a re-storage project at the Natural History Museum, London to reduce duplication of work (and handling) by staff and to combat the reduction in access caused by the enclosure of objects within microenvironments, which in turn helps preserve specimens for future access. This project demonstrates how conservation and digitisation can successfully synthesise through the use of barcodes, when working with a cross-discipline team.
    • Detecting foraminiferal photosymbionts in the fossil record: a combined micropalaeontological and geochemical approach

      Bhatia, R; Wade, B; Hilding-Kronforst, S; Spratt, J; Leng, M; Thornalley, D (2016-08-30)
    • Giant Sequoia: an extraordinary case study involving Carbopol® gel

      McKibbin, C; Allington-Jones, L; Verveniotou, E (Archetype Publishing LtdLondon, 2017-10-18)
      In 2016 a project was undertaken to stabilise and aestheticise the transverse section of giant sequoia on display at the Natural History Museum (NHM) in London, UK. This iconic specimen, which now dominates the top floor of the central hall, was 1300 years old when felled and has been part of the exhibitions for 122 years. Measuring over 4.5 metres in diameter, it posed many challenges during remedial conservation. The largest involved removal of the discoloured waxy substance and opacified shellac-based varnish that had been applied in the early 1980s. Solvent tests revealed that the coating was soluble in Industrial Methylated Spirits (IMS) and that the gel worked most effectively at a 1 hour application time. At longer durations the varnish itself gelled and the waxy component was re-deposited. The waxy substance was effectively removed by wiping with alternate white spirit and IMS swabs.
    • HYPERVELOCITY IMPACT IN LOW EARTH ORBIT: FINDING SUBTLE IMPACTOR SIGNATURES ON THE HUBBLE SPACE TELESCOPE

      Kearsley, AT; Colaux, JL; Wozniakiewicz, PJ; Gerlach, L; Anz-Meador, P; Liou, JC; Griffin, T; Reed, B; Opiela, J; Palitsin, VV; et al. (2018-04)
      HYPERVELOCITY IMPACT IN LOW EARTH ORBIT: FINDING SUBTLE IMPACTOR SIGNATURES ON THE HUBBLE SPACE TELESCOPE A T Kearsley 1,2,5, J L Colaux 3, D K Ross 4, P J Wozniakiewicz 2,5, L Gerlach 6, P Anz-Meador 4, J-C Liou 7, T Griffin 8, B Reed 8, J Opiela 4, V V Palitsin 3, G W Grime 3, R P Webb 3, C Jeynes 3, J Spratt 2, M J Cole 5, M C Price 5 and M J Burchell 5. 1 Dunholme, Raven Hall Road, Ravenscar, YO13 0NA, UK (kearsleys@runbox.com); 2 Natural History Museum (NHM), Cromwell Road, London, UK. 3 Ion Beam Centre, University of Surrey, Guildford, UK. 4 ESCG-Jacobs, NASA-JSC, Houston, TX, USA. 5 School of Physical Sciences, University of Kent, Canterbury, Kent, UK. 6 European Space Agency (ESA, retired), Noordwijk, The Netherlands. 7 NASA Johnson Space Center, Houston, TX, USA. 8 NASA Goddard Space Flight Center (GSFC), Greenbelt, Maryland, USA. ABSTRACT Introduction Return of large surface area components from the Hubble Space Telescope (HST) during shuttle orbiter service missions has allowed inspection of large numbers of hyper-velocity impact features from long exposure in low Earth orbit (LEO). Particular attention has been paid to the origin of the impacting particles, whether artificial Orbital Debris (OD) or natural Micrometeoroid (MM). Extensive studies have been made of solar cells (Graham et al., 2001; Kearsley et al 2005, Moussi et al., 2005) and recently, the painted metal surface of the Wide Field and Planetary Camera 2 WFPC2 radiator shield (Anz-Meador et al., 2013; Colaux et al., 2014; Kearsley et al., 2014a; Ross et al., 2014). Both of these materials from HST have layers of complex chemical composition, into which particle fragments and melt may infiltrate during impact. Experimental light gas gun (LGG) impacts (e.g. Price et al., 2014) have shown that impactor remains may be dispersed and dilute, often as a very thin and patchy coating within an irregular impact-generated pit. In previous studies, the low concentration of particle residue, the rugged topography of impact features, and especially the complex multi-element composition of the impacted surface were considered significant barriers to recognition of extraneous impactor-derived components. Analysis was both difficult and time consuming (e.g. Graham et al., 2001), and a substantial proportion of impactors (25-65%) could not be identified. Recent advances in energy dispersive X-ray microanalysis (EDX) now permit routine identification of impactor origins using scanning electron microscope (SEM); particle induced X-ray emission (PIXE) and micro-X-ray fluorescence (µ-XRF) instruments (Kearsley et al., 2012, 2014b). Here we demonstrate how these techniques have allowed impactor composition to be isolated, and the particle source determined for the great majority of WFPC2 samples studied. Methods To analyse impact melt on the zinc orthotitanate (ZOT) and aluminium alloy (Al-6061) of the WFPC2 radiator shield we used the Oxford Instruments INCA SEM-EDX spectrum pro-cessing software to separate peak and background X-ray counts for specified X-ray emission lines. From tables of likely OD and MM signature elements (e.g. Kearsley et al., 2005), and knowledge of the pristine WFPC paint and alloy compositions, we extracted data for the fol-lowing elements: Mg, Al, Si, S, K, Ca, Ti, Cr, Mn, Fe, Ni, Cu and Zn. Two types of graphical plot were developed, to highlight extraneous element signatures in small impacts on the ZOT paint (Fig. 1), and larger craters into the Al-alloy (Fig. 2). The impactor origin was then clas-sified by reference to a suite of decision trees (Kearsley et al., 2012). A Bruker X-Flash 6050 EDX detector was also used to obtain signal from the interior of deeper craters. PIXE maps and spectra were acquired in the Ion Beam Centre, University of Surrey (Colaux et al., 2014). Results Figure 1. WFPC2 impact feature 339: a) SEM backscattered electron (BE) image; b) SEM depth model; c) SEM-EDX maps show high Mg concentration in the impact melt lining the impact feature d) plots of SEM-EDX X-ray counts for Mg and Fe show much higher levels in impact melt (red) than in clean ZOT paint (blue), and a similar level to impact residue from LGG impacts of olivine grains (open black squares). Excess Mg and Fe contents in frothy impact melt show impactor was a micrometeoroid. Figure 2). WFPC2 impact feature 462: a) SEM BE image; b) SEM depth profile; c and d) PIXE EDX maps show Fe and Ni across crater pit and surrounding metal, some iron-rich in-clusions in the Al alloy, but Ni only enriched in pit; e) PIXE EDX spectra show high Fe and Ni on crater floor, similar to micrometeoroid metal composition; f) plot of Mg/Al versus Cr/Fe X-ray counts in SEM-EDX spectra from the crater edge (red) show enrichment of Mg and Fe over alloy composition (black, grey, yellow and green), indicating a mafic silicate mi-crometeoroid component has also been added from the impacted micrometeoroid. Summary and conclusions Together, SEM-EDX and PIXE-EDX maps, spectra and X-ray count plots showed 166 MM residues and 2 OD residues in this survey of 188 impact features on WFPC2, ~ 90% of those examined, considerable enhancement of impactor recognition over an earlier study of HST impacts (~75% identified as MM or OD in origin, Kearsley et al., 2005). Acknowledgements ESA contract 40001105713/12/NL/GE awarded to NHM and the University of Surrey; Bruker for expertise in use of the X-Flash detector and loan of the M4 Tornado µ-XRF. References quoted Anz-Meador P. et al. (2013) Proc. 6th European Conf. Space Debris, ESA SP 723: s1b_anzme.pdf, CD-ROM. Colaux J. L. et al. (2014) LPSC 45 Abstract #1727. Graham, G.A. et al. (2001) Proc. 3rd European Conf. Space Debris, ESA SP 473:197–203. Kearsley A.T. et al., (2005) Adv. Space Res. 35:1254–1262. Kearsley A. T. et al. (2012) Technical Note 1 for ESA contract 40001105713/12/NL/GE. Kearsley A. T. et al. (2014a) LPSC 45 abstract #1722. Kearsley A.T. et al. (2014b) LPSC 45 abstract #1733. Moussi A. et al. (2005) Adv. Space Res. 35:1243–1253. Price M. C. et al. (2014) LPSC 45 abstract #1466. Ross D. K. et al. (2014) LPSC 45 abstract #1514.
    • Impact vaporization and Condensation: Laser Irradiation Experiments with Natural Planetary Materials

      Hamann, C; Hecht, L; Schäffer, S; Heunoske, D; Salge, T; Garbout, A; Osterholz, J; Greshake, A (The Woodlands, Texas, USA, 2018)
    • Mechanisms for the generation of HREE mineralization in carbonatites: Evidence from Huanglongpu, China.

      Smith, M; Cangelosi, D; Yardley, B; Wenlei Song, CX; Spratt, J (The Society for Geology Applied to Mineral Deposits, 2019-12-30)
      The Hunaglongpu carbonatites, Qinling Mountains, China, are exceptional as they form both an economic Mo resource, and are enriched in the HREE compared to typical carbonatites, giving a metal profile that may closely match projected future demand. The carbonatites at the level currently exposed appear to be transitional between magmatic and hydrothermal processes. The multistage dykes and veins are cored by quartz which hosts a fluid inclusion assemblage with a high proportion of sulphate daughter or trapped minerals, and later stage, cross-cutting veins are rich in barite-celestine. The REE mineral paragenesis evolves from monazite, through apatite and bastnäsite to Ca-REE fluorcabonates, with an increase in HREE enrichment at every stage. Radio-isotope ratios are typical of enriched mantle sources and sulphur stable isotopes are consistent with magmatic S sources. However, Mg stable isotopes are consistent with a component of recycled subducted marine carbonate in the source region, The HREE enrichment is a function of both unusual mantle source for the primary magmas and REE mobility and concentration during post-magmatic modification in a sulphate-rich hydrothermal system. Aqueous sulphate is a none specific ligand for the REE, and this coupled with crystal fraction lead to HREE enrichment during subsolidus alteration.
    • The mineralogy of the effusive silicate rocks from the Mosonik volcano, Northern Tanzania.

      Sedova, AM; Zaitsev, AN; Spratt, J (Vernadsky Institute of Geochemistry and Anlytical Chemistry of Russian Academy of Sciences (GEOKHI RAS), 2018-10-01)
      International Conference on Magmatism of the Earth and Related Strategic Metal Deposits 3-7 September, 2018 Vernadsky Institute of Geochemistry and Analytical Chemistry of Russian Academу of Sciences, Moscow, Russia. The mineralogy of the effusive silicate rocks from the Mosonik volcano, Northern Tanzania Sedova А.М.1, Zaitsev A.N.1,2, J. Spratt2 1 Department of Mineralogy, St. Petersburg State University, Saint-Petersburg, Russia, e-mail: a.sedova@spbu.ru 2Department of Core Research Laboratories, Natural History Museum, London, UK The Mosonik volcano belongs to the Neogene-Resent volcanics of the Natron-Engaruka region of the East African Rift system. It is one of several stratovolcanoes located on the northeastern tip of the Gregory Rift Valley. Mosonik is attributed as having the earliest phase of eruptions in this province (Dawson, 2008) and is dated in the range 3.18-1.28 Ma (Isaac & Curtis, 1974; Dawson, 2008). In 1961, it was mapped by the Tanganyika Geological Survey (Guest et al., 1961), with published data (Paslick et al., 1996) on the composition of minerals from basanites, nephelinites and phonolites. According to the results of this study the compositions of melilite and nephelinite, Zaitsev et al. (2015) have indicated that the Mosonik volcano could be a potential source for the Upper Laetolil Footprint Tuff 7. According to our data the main effusive rocks of Mosonic are various nephelinites and phonolites, quite often they contain xenoliths of plutonic rocks: melteigites, foyaites, ijolites, and rocks of the enclosing stratum (andesites). Carbonatites mostly occur as boulders of various sizes within creek deposits. Among nephelinites there are nephelinites s.s., phonolitic nephelinites, calcite-phonolite nephelinites and melilite nephelinites. Microphenocrysts are represented by nepheline (45-60%), pyroxenes of diopside-hedenbergite solid solution, in some cases with aegirine edging (15-30%), apatite (3-10%) and titanite (3-10%). Calcite content reaches 10% within the calcite varieties of nephelinites; sanidine up to 10% in phonolitic nephelinites, which are strongly altered. Melilite nephelinites are also characterized by the following coposition: melilite (20%), perovskite (5%), sherlomite (3%). In rare cases within the nephelinites there are microphenocrysts of nepheline. Phonolites are represented by the following species: phonolites, sodalite phonolites and calcite phonolites. Phenocrysts are represented by nepheline (40-65%), pyroxenes of the diopside-hedenbergite series, rarely with aegirine edging (10-50%), sanidine (15-40%), Mg-Fe mica (0-5%), titanite (1-10%), and apatite (0-8%). In these rocks a large number of macrophenic crystals of nepheline, pyroxene, and often sanidine are observed. The work is supported by Russian Foundation of Basic Research (grant 18-05-00835) and St. Petersburg State University (Geomodel Resource Center) References Dawson J. B. The Gregory Rift Valley and Neogene-Recent Volcanoes of Northern Tanzania. London. 2008. 112 pp. Guest N. J., James, T. C Pickering R., and Dawson J. B. Angata salei. Geol. Surv. Tanganyika. Quarter degree sheet 39. 1961 Isaac, G. L. & Curtis, G. H. Age of the Acheulian industries from the Peninj Group, Tanzania // Nature. 1974. p.249. Paslick, C., Halliday, A. N., Lange, R. A., James, D. & Dawson, J. B. Indirect crustal contamination: evidence from isotopic and chemical disequilibria in minerals from alkali basalts and nephelinites from northern Tanzania // Contributions to Mineralogy and Petrology. Vol. 125. 1996. 277–292. Zaitsev A.N., Spratt J., Sharygin V.V., Wenzel T., Zaitseva O.A., Markl G. Mineralogy of the Laetolil Footprint Tuff: A comparison with possible volcanic sources from the Crater Highlands and Gregory Rift // Journal of African Earth Sciences. Vol. 111. 2015. pp. 214–221.
    • Porphyry Cu(Mo) deposits of the Urals: insights from molybdenite trace element geochemistry

      Plotinskya, OP; Abramova, VD; Bondar, D; Seltmann, Reimar; Spratt, J (The Society for Geology Applied to Mineral Deposits, 2019-10-01)
      The first data on EMPA and LA-ICPMS study of molybdenite from four porphyry deposits of the South and Middle Urals (Tomino, Mikheevskoe and Benkala porphyry Cu and Talitsa porphyry Mo deposits) are presented. It is shown that most trace elements form mineral inclusions within molybdenite in all the deposits studied; only Re and W are most likely to be incorporated into the molybdenite lattice. Porphyry Cu deposits (Tomino and Mikheevskoe) formed within oceanic arc settings are featured by high contents of Re (mostly over 400 ppm) and low contents of W (<10 ppm) in molybdenite; porphyry Cu deposits from Andean-type geotectonic environment (Benkala) are featured by lower Re content (hundreds ppm) and high contents of W (tens ppm) in molybdenite. Molybdenite from porphyry deposits from collisional setting (Talitsa) has low content of Re and elevated W contents (tens ppm). It is demonstrated that trace element geochemistry of molybdenite is a useful tool to define the source of metal components and the geotectonic environment for porphyry Cu(Mo) deposits.
    • The remedial conservation and support jacketing of the neotype specimen of the dinosaur Massospondylus carinatus

      Graham, M (PeerJ, 2017-08-09)
      The remedial conservation and support jacketing of the neotype specimen of the dinosaur Massospondylus carinatus
    • Sadiman Volcano, Crater Highlands, Tanzania; does it really contain melilitites and carbonatites or its is just a phonolite-nephelinite volcano?

      Zaitsev, AN; Wenzel, T; Markl, G; Spratt, J; Petrov, SV; Williams, CT (Department of Mineralogy, Geochemistry and Petrology, University of Szeged, Szeged, Hungary, 2012)
      Sadiman is 4.8-4.0 Ma old volcano located in the Crater Highlands area in northern Tanzania. Limited published data and field observations show that it consists of interlayered phonolitic tuffs and nephelinitic lavas. Rare xenoliths of phonolite and ijolite were observed in the nephelinites. It was suggested that Sadiman volcano contains melilititic and carbonatitic rocks. These also occur as tuffs in the Laetoli area where fossilised footprints from human ancestors are known which is why Sadiman is of special interest as a possible source of them.
    • Zircon-hosted apatite inclusions: A powerful tool for reconstruction of Cl contents in melts

      Tuffield, L; Buret, Y; Large, S; Spratt, J; Wilkinson, JJ (Mineral Deposits Studies Group, 2020-01)
      Chlorine in the exsolved volatile phase plays an important role in complexing with metals in the extraction and concentration of metals in magmatic-hydrothermal ore deposits. Therefore, tracking the concentration and evolution of Cl in the parent melt is of particular importance in understanding how such deposits form. In theory, the incorporation of Cl into apatite could be used to track the volatile content of melts; however, low closure temperatures and the rapid diffusion of halogens in apatite make it susceptible to sub-solidus re-equilibration by later thermal events and hydrothermal fluids. This susceptibility compromises its ability to retain the primary halogen signature. However, the common occurrence of apatite as an inclusion phase in zircon crystals, together with the refractory nature of zircon, open up the possibility that such inclusions may preserve primary Clmelt compositions [1]. The Rio-Blanco-Los Bronces porphyry copper district is located in central Chile and hosts several world class porphyry copper deposits as well as barren intrusions [2]. This makes it an excellent area for an investigation of the role of Clmelt in the formation of porphyry copper deposits, as well as the effect of sub-solidus re-equilibration of Cl in apatite. For this study we analysed apatite crystals that occur both in the groundmass and as inclusions in zircons in four samples from the Los Bronces porphyry copper district using EPMA for halogen and major elements and LA-ICP-MS for trace elements. These samples include a barren intrusion unrelated to mineralisation that precedes mineralisation by around 10 Ma, and pre-, syn- and post-mineralisation porphyries. Apatite inclusions hosted in zircon crystals typically exhibit a large range in Cl concentrations (<0.5 –2.5 wt.% Cl), with all inclusion data exhibiting polymodal distributions of Cl concentrations. By contrast, groundmass apatites from all samples are characterised by uniformly low Cl concentrations (<0.5 wt.% Cl). These results are consistent with the apatite crystals in the groundmass having experienced sub-solidus re-equilibration related to the pervasive hydrothermal alteration in the district. The wide range in Cl concentrations recorded by the apatite inclusions is interpreted to reflect changing Clmelt for the duration of apatite and zircon crystallisation, perhaps linked to volatile saturation and preferential partitioning of Cl into the aqueous phase. Additionally, the apatites hosted in zircon crystals show significant inter-sample variations, evolving from low Cl concentration (<0.5 wt. % Cl) in the barren intrusion, to higher Cl concentrations (0.5 – 2.5 wt.% Cl) in the samples closely temporally associated with porphyry Cu mineralisation. These data suggest that Clmelt was significantly higher (0.05 – 0.40 wt.% Clmelt) in the melts associated with porphyry copper mineralisation compared with the precursor barren magmatism (~0.04 wt.% Clmelt) [3]. We conclude that due to the rapid diffusion of halogens in apatite in the presence of melt or hydrothermal fluid, the study of apatite inclusions hosted in zircon crystals is required to reconstruct primary melt compositions and to track the evolution of Cl concentrations in porphyry-forming magmas. This study reveals high Clmelt concentrations in the magmas related to mineralisation in the Los Bronces district, a property that would have facilitated the efficient extraction and concentration of metals. References: [1] Brugge, E. et al. (2019). Proc. 15th SGA Biennial Meeting, Vol. 2, 983-986. [2] Toro, J.C. et al. (2012). SEG Special Publication 16:105-126. [3] Li, H. and Hermann, J. (2017) Am. Mineral. 102:580-594.