Post-magmatic Alteration Processes Research Articles

Multi-mode chemical exchange in seafloor alteration revealed by lithium and potassium isotopes

Elemental exchange during seafloor alteration exerts substantial control on the chemical compositions of seawater and oceanic crust, as well as the global elemental cycling. However, detailed processes and mechanisms for element transport and isotopic exchange remain unclear. Here, we report Li and K isotopic compositions across an altered MORB-like pillow basalt from Mariana Trench. We find large and systematic isotopic variations on a centimeter scale, with δ7Li decreasing from +9.07‰ to +6.21‰ and δ41K increasing from −0.12‰ to +0.33‰ from the rim to the core. The heavier-than-mantle Li and K isotopic compositions in the core likely inherit from an enriched mantle source rather than post-magmatic alteration processes. The low K and high Li isotopic compositions at the outmost rims result from adsorption during seawater-rock interactions. The basin-shaped elemental and isotopic variations were subsequently formed by chemical diffusion and spontaneous seawater penetration from the weathered rind to the interior of pillow basalt sample. This study uses a small-scale sampling approach and provides the first evidence for multi-mode chemical exchange in oceanic basalts and improves our understanding of the seafloor alteration processes.

The use of assay data as a foundation for a geometallurgical model—The case of the Thaba Chromite Mine, South Africa

The Lower and Middle Group chromitites of the Bushveld Igneous Complex in South Africa are the source of a very large portion of the global chrome supply. The recovery of platinum group elements and base metals (Ni, Cu) as by-products has the potential to add value to these chrome resources. Yet, the effectiveness of chromite and platinum-group element beneficiation circuits is highly sensitive to variations in feed composition. Of particular relevance is the abundance of alteration silicates, which have a negative impact on recoveries and concentrate grade. The use of geochemical proxies, based on data acquired routinely during the exploration and mining process may provide a cost- and time-efficient alternative to more time-consuming and expensive mineralogical analyses. Such an approach is presented in this study, which focuses on the LG-6, LG-6A, MG-1 and MG-2 chromitite seams at the Thaba mine located on the western limb of the Bushveld Complex. An extensive assay data set comprising of data for Cr2O3, FeO, Al2O3, MgO, SiO2, CaO and P provided by the mine owner was evaluated and corrected for systematic bias between different sample batches. A statistical assessment was performed to discuss the variability within and between the chromitite seams and to separate the mine lease area into distinct geochemical clusters. The distribution of the samples belonging to the different geochemical clusters was then transposed onto the geology of the mine lease area. This allowed the definition of spatial domains. These spatial domains, recognized by the assessment of assay data only, are then validated by mineralogical attributes; implications for mineral beneficiation are critically assessed. According to this assessment, the chromitites of the Thaba mine area can be subdivided into three distinct domains, domains that constitute the suitable fundament for a geometallurgical model. An extensive supergene altered domain is distinguished from a domain affected by hydrothermal alteration. The latter domain occurs below the depth of modern weathering, but in obvious proximity to faults and around a prominent dunite pipe. The third domain is represented by ores least affected by post-magmatic alteration processes. This domain occupies the centre of fault blocks below the extent of modern weathering.

Geochemistry of mafic–ultramafic magmatism in the Western Ghats belt (Kudremukh greenstone belt), western Dharwar Craton, India: implications for mantle sources and geodynamic setting

ABSTRACTWestern Ghats Belt of western Dharwar Craton is dominated by metavolcanic rocks (komatiites, high-magnesium basalts (HMBs), basalts, boninites) with occasional metagabbros. This rock-suite has undergone post-magmatic alteration processes corresponding to greenschist- to lower-amphibolite facies conditions. Komatiites are Al-depleted, characterized by lower Al2O3/TiO2 and high CaO/Al2O3. Their trace element distribution patterns suggest most of the primary geochemical compositions are preserved with minor influence of post-magmatic alteration processes and negligible crustal contamination. Chemical characteristics of Al-depleted komatiites imply their derivation from deeper upper mantle with/without garnet involvement. HMBs and basalts are differentiated based on their magnesium content. Basalts and occasionally associated gabbroic sills have similar geochemical characteristics. HMB are characterized by light rare earth element (LREE) enrichment, with significant Nb–Ta and Zr negative anomalies. Basalts and associated gabbros display tholeiitic affinity, with LREE-enriched to slightly fractionated heavy rare earth element (HREE) patterns. Boninites are distinctive in conjunction of low abundances of incompatible elements with respect to the studied komatiites. Chondrite-normalized REE patterns of boninites show relative enrichment in LREE and HREE with respect to MREE. Prominent island arc signatures are evident in HMB, basalts, boninites, and gabbros in terms of their Nb–Ta and Zr–Hf negative anomalies, LREE enrichment and HFSE depletion. It is suggested that these HMB–basalts (associated gabbros)–boninites are the products of arc magmatism. Their REE chemistry attests to a gradual transition in melting depth varying between spinel and garnet stability field in an arc regime. The close spatial association but contrasting elemental characteristics of komatiites and HMB–basalts–boninites can be explained by a plume-arc model, in which the ~3.0 Ga komatiites are considered to be the products of plume volcanism in an oceanic setting, while the HMB, basalts, boninites, and associated gabbros were emplaced in a continental margin setting around 2.8–2.7 Ga.

Geochemistry of the uranium-thurium-bearing granitic rocks and pegmatites of wadi haleifiya area, southeastern Sinai, Egypt

There are two main granitic rocks cropping out in the study area: 1) the syn-orogenic granites are moderately weathered, jointed, exfoliated and characterized by low relief. These rocks are subdivided into tonalite and granodiorite. They are essentially composed of plagioclase, quartz, biotite, hornblende and potash feldspar; and 2) the post-orogenic granites, characterized by high relief terrain and represented by monzogranite, syenogranite and alkali granite. The monzogranites suffered hydrothermal alteration in particular along joints, faults, shear zones and fractures, which recorded the highest values of radioactivity, reflecting the role of post-magmatic alteration processes in the enhancement of radioactivity. The hydrothermal alteration (desilicification and hematitization) resulted in the formation of mineralized (altered) granites. The altered granites are enriched in TiO2, Al2O3, FeOT, MnO, MgO, Na2O, Rb, Sr, Y, Zr, Zn, Ga and Co and depleted in SiO2, CaO, P2O5, Nb, Pb, Cu, Ni and Cr relative to the fresh monzogranite. The investigated granites contain basic xenoliths as well as pockets of pegmatites. Perthites, quartz, plagioclase and sometimes biotite, represent the essential constituents. Some accessory minerals like zircon are metamicted reflecting their radiogenic nature. The alkali granites are characterized by the presence of aegirine, rebeckite and arfvedsonite. Both syn- and post-orogenic granites show some variations in their bulk chemical compositions. The older granitoids are metaluminous and exhibit characteristics of I-type granites and possess an arc tectonic environment. On the other hand, the younger granites are peraluminous and exhibit the characteristics of post-collisional granites.It is interpreted that radioactivity of the studied rocks is mainly controlled by both magmatic and post-magmatic activities. Frequently, the post-orogenic granites host zoned and unzoned pegmatite pockets. Some of these pockets anomalously attain high radioactivity. The syenogranites and the pegmatites are characterized by high contents of SiO2 and K2O and low CaO and MgO. They have transitional characters from highly fractionated calc-alkaline to alkaline. The alkali granites related to A2-subtype of A-type granites. The post-orogenic granites were originated from magma of dominant crustal source materials and related to post-collisional setting under extensional environment.

A Ocorrência Alcalina de Cananeia, Litoral Sul do Estado de São Paulo: Química Mineral

A ocorrência alcalina de Cananeia, de idade Cretáceo Superior (Ar-Ar, 83,6 Ma), localiza-se no Vale do Ribeira e é representada por dois pequenos corpos: Morro de São João (1,8 km²), na Ilha de Cananeia, e Morrete (0,4 km²), na vizinha Ilha Comprida. Ela é coberta por sedimentos quaternários e constituída dominantemente por rochas intrusivas de natureza sienítica, reunidas em dois grupos principais: álcali feldspato sienitos e quartzo-álcali feldspato sienitos. Microssienitos com textura variada ocorrem subordinadamente. Quanto à mineralogia, as rochas apresentam grande riqueza em feldspatos, sendo mesopertita a fase mais abundante, e plagioclásio, na forma de cristais isolados, de presença tão-somente ocasional. Os máficos consistem dominantemente em clinopiroxênios e anfibólios, enquadrados nos grupos cálcico, cálcico-sádico e sádico, mostrando variações químicas expressivas, que se traduzem principalmente no aumento da relação Fe/Mg e do teor em Na, e da diminuição da concentração em Ca, em função do grau de evolução das rochas. Relações texturais indicam a transformação clinopiroxênio → anfibólio. Biotitas são comuns, sobretudo em associação com anfibólio e opacos, quando ocupam as porções periféricas dos grãos do primeiro mineral e se concentram ao longo de suas fraturas e planos de clivagem. Olivinas, de natureza faialítica, estão raramente preservadas. Os principais acessários incluem opacos, essencialmente magnetita com lamelas exsolvidas de ilmenita, apatita, titanita e zircão. Processos de alteração tardi a pás-magmática podem explicar as texturas de substituição encontradas nos principais minerais primários, bem como as estruturas de exsolução presentes nos feldspatos e opacos.

3.35 Ga komatiite volcanism in the western Dharwar craton, southern India: Constraints from Nd isotopes and whole-rock geochemistry

We present field, petrographic, Sm–Nd whole-rock isochron and whole-rock geochemical data for komatiites from Sargur Group greenstone belts of the western Dharwar craton. Field evidence such as pillow structure indicates their eruption in a marine environment. Petrographic data reveal that the igneous mineralogy has been altered during post-magmatic hydrothermal alteration processes corresponding to greenschist- to lower amphibolite facies conditions with rarely preserved primary olivine and orthopyroxene. A 16-point Sm–Nd whole-rock isochron gives an age of 3352 ± 110 Ma for the timing of eruption of komatiite lavas. About 60% of the studied komatiite samples show Al-depletion whilst the remaining are Al-undepleted. The Al-depleted komatiites are characterised by high CaO/Al 2O 3 ratios (1.01–1.34) and low Al 2O 3/TiO 2 (5–16) whereas Al-undepleted komatiites show lower CaO/Al 2O 3 ratios (0.59–0.99) and higher Al 2O 3/TiO 2 (17–26). Trace element distribution patterns of komatiites suggest that most of the primary geochemical and Nd isotopic compositions are preserved with only minor influence of post-magmatic alteration processes and negligible crustal contamination. The chemical characteristics of Al-depleted komatiites, such as high (Gd/Yb) N together with lower HREE, Y, Zr and Hf, imply their derivation from deeper upper mantle with garnet (majorite?) involvement, whereas lower (Gd/Yb) N slightly higher HREE, Y, Zr and Hf suggest derivation from shallower upper mantle without garnet involvement. The observed chemical characteristics (CaO/Al 2O 3, Al 2O 3/TiO 2, MgO, Ni, Cr, Nb, Zr, Y, Hf, REE) indicate derivation of the komatiite magmas from different depths in a plume setting, whereas sub-contemporaneous felsic volcanism and TTG accretion can be attributed to an arc setting. In order to explain the spatial association of komatiite volcanism with contemporaneous mafic-felsic volcanism and TTG accretion we propose a combined plume-arc setting. Nd isotope data of the studied komatiites indicate depleted mantle reservoirs which may have evolved by early (>4.53 Ga) global differentiation of the silicate Earth as suggested by Boyet and Carlson [Boyet, M., Carlson, R.W., 2005. 142Nd evidence for early (>4.53 Ga) global differentiation of silicate Earth. Science 309, 577–581] or extraction of continental crust during the early Archaean.

Geochemical and isotopic (Sr, C, O) data from the alkaline complex of Gr�nnedal-?ka (South Greenland): evidence for unmixing and crustal contamination

The alkaline intrusion of Gronnedal-ĺka (South Greenland) is the oldest of the ten major rift-related plutonic complexes of southern Greenland that intruded during the Gardar period between 1330 and 1150 Ma into the 2.6-Ga-old gneisses and metasediments of the Ketilidian basement. The Gronnedal-ĺka alkaline intrusion consists of carbonatites, silicocarbonatites, transitional carbonatites and nepheline-bearing syenites. The silicocarbonatites exhibit locally ocellar textures that are typical for immiscibility processes. A 87Sr/86Sr initial ratio of about 0.703184 major and trace element compositions—including REE and C-, and O-isotope data from 15 carbonatite, 12 silicocarbonatite, 10 transitional carbonatite and 8 syenite and samples—provide evidence for minor crustal contamination of the mantle-derived magma that generated by unmixing carbonatites, silicocarbonatites and syenites. A scatter in major and trace element contents and isotope ratios is related to late- to post-magmatic alteration processes. The Gronnedal-ĺka silicocarbonatites are one of the rather rare cases in which unmixing of a highly alkaline mantle-derived magma into an alkalisilicate and a carbonatitic magma-fraction under plutonic conditions is well documented by textural and geochemical data.

Contrasting geochemical patterns in the 3.7–3.8 Ga pillow basalt cores and rims, Isua greenstone belt, Southwest Greenland: implications for postmagmatic alteration processes

Pillow basalts from the early Archean (3.7 to 3.8 Ga) Isua greenstone belt, West Greenland, are characterized by well-preserved rims and concentric core structures. The pillow rims and cores have different mineral assemblages, and chemical and isotopic compositions. The rims have systematically higher contents of Fe 2O 3, MgO, MnO, K 2O, Rb, Ba, Ga, Y, and transition metals than the cores. In contrast, the cores possess higher concentrations of SiO 2, Na 2O, P 2O 5, Sr, Pb, U, Nb, and the light rare earth elements (REEs than the rims). These compositional variations in the rims and cores are likely to reflect the mobility of these elements during posteruption alteration. Variations of many major and trace element concentrations between the rims and cores of the Isua pillow basalts are comparable to those of modern pillow basalts undergoing seafloor hydrothermal alteration. Al 2O 3, TiO 2, Th, Zr, and the heavy REEs display similar values in both rims and cores, suggesting that these elements were relatively immobile during postemplacement alteration. In addition, the rims and cores have distinctive Sm-Nd and Rb-Sr isotopic compositions in that the rims are characterized by higher 143Nd/ 144Nd and 87Sr/ 86Sr ratios than the cores. The pillow basalts yield 2569 ± 170 Ma and 1604 ± 170 Ma errorchron ages on 143Nd/ 144Nd vs. 147Sm/ 144Nd and 87Sr/ 86Sr vs. 87Rb/ 86Sr diagrams, respectively. The Sm-Nd errorchron age may correspond, within errors, to a late Archean tectonothermal metamorphic event recorded in the region. The Sm-Nd errorchron may have resulted from a combination of isotopic homogenization and preferential loss of Nd, relative to Sm, during late Archean metamorphism. Although the Rb-Sr errorchron age overlaps with the timing of an early to mid-Proterozoic tectonothermal metamorphic event recorded in the region, because of a considerably large mean square of weighted deviates value and scatter in 86Sr/ 87Sr and 87Rb/ 86Sr ratios, this age may not have a precise geological significance. The 1.6 Ga Rb-Sr errorchron is likely to have resulted from the loss of radiogenic 87Sr. Collectively, the Sm-Nd and Rb-Sr data obtained from the 3.7–3.8 Ga Isua pillow basalt rims and cores are consistent with disturbances of the Sm-Nd and Rb-Sr systems by tectonothermal metamorphic events long after their eruption. In contrast to the Sm-Nd and Rb-Sr systems, the Lu-Hf system appears to be largely undisturbed by metamorphism. Five core samples and three rim samples yield a 3935 ± 350 Ma age, within error of the approximate age of eruption (3.7 to 3.8 Ga). Two rim samples that have gained Lu give an age of 1707 ± 140 Ma, within error of the Rb-Sr errorchron age. Initial 176Hf/ 177Hf ratios of the undisturbed samples at 3.75 Ga lie within ±1 ε-unit of the chondritic value, suggesting no long-term depletion in the mantle source of the basalts.

A review of the occurrence and origin of abiogenic hydrocarbons in igneous rocks

Abstract Reports on the presence of hydrocarbons in igneous rocks have been on the increase and generating greater interest in the scientific community over the last 20 years. Most of the occurrences are due to the incorporation of organic material into the magmatic systems. However, reports on the presence of hydrocarbons formed by abiogenic processes have also increased in recent years, suggesting that these hydrocarbons may not be as rare as previously thought and may have implications for natural gas resources in the future. This paper reviews these occurences and the models proposed for the generation of these hydrocarbons, in particular the nature of the hydrocarbon-bearing fluids in the alkaline complexes Khibina, Lovozero and Ilímaussaq. The origin of these hydrocarbons remains controversial, whether they are (1) derived directly from the mantle, (2) formed during late crystallization stages by respeciation of a C-O-H fluid below 500°C, or (3) formed during postmagmatic alteration processes involving Fisher-Tropsch type reactions catalysed in the presence of Fe-oxides and silicates. The reports suggest that a direct mantle origin for the hydrocarbon fluid is unlikely. A model involving near-solidus reequilibration of a C-O-H fluid to a CH 4 -rich composition is possible, although only for extreme melt compositions that have large crystallization temperature ranges (i.e. hyperagpaitic melts). The Fischer-Tropsch synthesis of hydrocarbons in igneous rocks seems to be a more applicable model for a wide variety of igneous rocks.

CRONOLOGIA DAS ALTERAÇÕES PÓS-MAGMÁTICAS ASSOCIADAS AO MACIÇO GRANÍTICO DA SERRA BRANCA - GOIÁS

The Serra Branca pluton, of medium Proterozoic age is situated in the Tocantins sub-province of the Tin Province of Goias ; is composed by a several differenciatted grariite types: a biotite-granite, predominam in the W part of the massif, a two-mica granite and a muscovite granite. A small topaz granite is the most evolved type that outcrops in the Eastern part of the massif. The intense differentiation of the massif makes itself on an asymetrical manner due to the development of post-magmatic alteration processes that culminated with the formation of massive greisens. Ali rocks of the pluton (granite and greisens) together with the surrounding quartzites and quartz-micaschists of the Arai Groupe have been deformed and largelly recristallized during the Brasiliano tectono-metamorphic event. This deformation, as well as the intensity of the post-magmatic alterations, increases from W to E of the pluton. The relative importance of the hydrothermal alterations (s.l.) developed on the different types of the pluton manifests itself, chronologically, by located albitization, followed by greisenization and, by late microclinization that indiscriminately hits ali the granitic and greisens types of the pluton. The main minerais of economical interest related to the greisenization episode are cassiterite, topaz and beryl. This alteration have strongly modified the original geochemical signatures of the granites. Chemical variations are mainly the expressions of those superimposed modifications.

Mise en évidence d'un volcanisme alcalin intraplaque d'âge Acadien dans la Meseta nord-occidentale (Maroc)

Abstract In northwestern Meseta, the Sidi-Said Maâchou volcanic complex includes dykes, sills and basaltic flows. This volcanism is synchronous with a Paradoxides schist deposit. Most of the rocks have been affected by post-magmatic alteration processes, which have modified their major and trace elements composition. The geochemical characteristics can be discussed on the basis of the high field strength elements, transition elements, Th, Ta and rare earth elements. Hence, the Sidi-Said Maâchou dolerites consist of within-plate alkali volcanism. This volcanism and those recognised in the Anti-Atlas, High-Atlas and eastern Meseta suggest a Cambrian extensive episode during the break-up of the palaeo-Gondwana supercontinent.

Mineral Chemistry of Albite-Enriched Granitoids at Um Ara, Southeastern Desert, Egypt

Mineral chemistry and typomorphic characteristics are used to monitor the physicochemical evolution of late-magmatic to postmagmatic alteration processes that resulted in the development of a radioactive and albite-enriched microgranite stock. The mineral paragenesis indicates that postmagmatic fluids were enriched in Nb, Zn, Mn, U., Th, Zr, and Y, in addition to Rb, Li, and F Manganocolumbite with extremely high Nb/(Nb+Ta) (0.99), Mn/(Mn+Fe) (0.82), and zircon with high Zr/(Zr+Hf) (0.97) indicate crystallization under alkaline, relatively high-temperature conditions (>425° C). The close association of manganocolumbite, Nb-Mn-Zn- rich ilmenite (with 1.2 to 14.5 wt% ZnO), spessartine garnet (with 68.2-89.4 mol% spessartine), zircon, xenotime, zinnwaldite mica (up to 5.98 wt% F), and fluorite indicates the strong affinity of the elements of Nb, Y., Zr, Mn, and Zn for stable complexing by K+, Na+, Li+, and F− rich supercritical fluids during the course of extraction and transportation. The enrichment of the interacting fluid in U and Th is depicted by the presence of up to 1.6% UO2 in manganocolumbite and Hf-bearing zircon, and up to 10.5% ThO2 in monazite, in addition to locally abundant thorite and uranophane. It is suggested that the uranium mineralization, mainly as fracture fillings, formed during the waning stage of hydrothermal activity.

Dredged basalts from the western Nazca plate and the evolution of the East Pacific Rise

Ocean-floor basalts and glasses were recovered from three stations along the western Nazca plate, from a sublinear topographic feature believed to represent the proto-East Pacific Rise (EPR), and include abyssal tholeiites, FeTi-basalts and glasses, as well as transitional and little fractionated compositions. When compared with their coexisting fresh glasses, the FeTi-basalts have higher total alkalies, TiO 2 and MgO, and lower FeO *, suggesting that they have also been affected by non-oxidative post-magmatic alteration processes. The FeTi-glasses form a remarkably uniform compositional group through space and time. A little fractionated composition having an Mg-number= 73, similar to those reported from the Mathematician Ridge, has higher Na 2O and TiO 2, and slightly lower CaO than similar compositions from the slowly accreting Mid-Atlantic Ridge. The basalts and glasses reported here exhibit the compositional diversity expected for propagating rifts and probably represent more than one volcanic episode. Both geochemical and geophysical interpretations support the inference that the EPR grew from Miocene times by the progressive growth and propagation of mantle perturbations, leaving a remnant sublinear zone of rough topography characteristic of slower accretion as the trace of the proto-EPR. Continuing translations and rotations of axial segments are occurring along the EPR, probably in response to self-reorganizations of mantle flow patterns arising from rapid melting and depletion of the source regions. The data allow the inference that the youthful rift systems of the eastern Pacific are far from thermodynamic equilibrium as might be expected if such systems were to drive fundamental life processes.

Petrochemistry and tectonic significance of the Highland Border Suite mafic rocks

The metamorphosed mafic rocks of the ophiolitic Highland Border Suite on Arran and Bute are of 2 types: greenschist facies pillow lavas and epidote-amphibolite facies hornblende schists, respectively. Both types have been affected by post-magmatic alteration processes, including spilitization (i.e. Na-enrichment coupled with Ca-depletion). On the basis of 'immobile element' chemistry and other criteria, the mafic rocks are split into 2 (magmatic) groups: a tholeiitic one which shows the effects of extensive low-pressure fractionation (e.g. Fe- and Ti-enrichment), and a less-fractionated alkaline group that contains relict Al- and Ti-rich clinopyroxenes. The tholeiitic rocks are similar to modem ocean-floor or marginal-basin basalts, and the alkaline rocks show affinities with 'within-plate' basalts. This 'magma-type' and 'tectonic-setting' dichotomy is found at other Highland Border localities and is present in both the pillow lavas and hornblende schists. The Highland Border Suite mafic rocks may have formed as tholeiitic ocean-basin crust upon which alkaline ocean-island lavas had been erupted, or alternatively, as is suggested in this paper, they may have formed during the early stages of development of a pre-Grampian marginal basin of Cambrian (or Cambro-Ordovician) age.

Ultramafic rocks of the Widgiemooltha-Norseman area, Western Australia: Petrological diversity, geochemistry and mineralisation

Mineral exploration of the Widgiemooltha-Norseman region of Western Australia has located massive and disseminated nickel sulphide mineralisation. This paper discusses the geological setting of the nickel sulphide mineralisation with reference to the stratigraphy, structure and metamorphism of the ultramafic sequence and spatially associated rocks. The amphibolite facies metamorphosed ultramafic rocks of the Widgiemooltha area are compared with greenschist metamorphosed ultramafic rocks at Eundynie, which exhibit excellently preserved pseudomorphs of primary igneous textures. Some 2000 ultramafic rock samples were analysed for 13 element/oxides and divided into four major mineralogically and texturally distinct groups. The data were analysed statistically by determination of means and standard deviations and multiple regression analyses. The data suggest differentiation of a magma at depth followed by a vast outpouring of lava to produce picritic-peridotitic rocks. The flows crystallised with upper spinifex zones and lower euhedral-olivine zones in varying proportions dependent on magma composition. The development of spinifex texture is compositionally controlled. This texture is not developed in rocks with MgO contents greater than 26% (± 2%). The comparison of the ultramafics of the Widgiemooltha and Eundynie areas indicates that talc-carbonate formation and serpentinization have modified primary igneous textures and geochemistries, resulting in the production of a diverse group of rock types. Such post-magmatic alteration processes in association with structural elements are considered important in the upgrading of nickel sulphide mineralisation.