This study aims at understanding parental melt compositions and evolutionary history of mantle-derived kimberlitic magmas, using unaltered Udachnaya-East kimberlite as an example. Recent advances in theoretical, experimental and melt inclusion research strongly suggest that the mantle is highly heterogeneous on a small scale, but this heterogeneity is effectively obscured by the blended nature of most erupted magmas. Thus, the original compositions of individual mantle-derived melt batches that supposedly reflect their respective mantle sources are in fact averaged, owing to mixing of melts en route to the surface. The exception may be occasional low degree partial melts that erupt with little or no mixing with subsequent melt fractions. However, such melts are particulary prone to reaction with country rocks along the pathways to ascent, and are also very rare among erupted rocks. Among all known erupted mantle-derived magmas, kimberlites offer the deepest probes into the convecting subcontinental mantle, derived from the lowest degrees of melting. Such origins make kimberlites most suitable for characterising primitive (undepleted by previous melting) mantle assemblages with their likely enrichment in the volatile elements, and thus with the lowest solidus temperatures. On the other hand, the large amount of lithospheric and crustal xenoliths in kimberlites and their typically high degree of alteration, can significantly affect interpretations that can be drawn from bulk rock analyses. This study attempts to overcome such problems related to alteration of kimberlites and presents detailed petrographic, mineralogical, chemical, and isotope data on exceptionally fresh kimberlite samples from the diamondiferous Udachnaya-East pipe (Daldyn-Alakit region, Siberia). I demonstrate that the Udachnaya-East rocks have radiogenic isotopic compositions, petrographic features and major and trace element geochemistry typical of group-I kimberlites. However, unlike common kimberlites, the studied samples show no primary or secondary serpentine, and thus are essentially anhydrous (< 0.5 wt% H2O), but CO2-rich (10-11 wt%). In contrast with other kimberlites worldwide, the Udachnaya-East samples are uniquely enriched in chlorine and alkalies (2.3-3.2 wt% Cl, 2.6-3.7 wt% Na, and 1.6-2.0 wt% K). Enrichment in CO2, Cl and alkalies is expressed in the essentially alkali-carbonate (shortite, zemkorite) and alkali-chloride (halite, sylvite) composition of the kimberlite groundmass. These minerals cement olivine phenocrysts and form round segregations ("nodules"). Radiogenic isotope compositions (Nd, Sr, and Pb) of the chloride, chloride - alkali carbonate, carbonate and oxide-silicate constituents in the groundmass of the Udachnaya-East kimberlite effectively show the coexistence of these phases in the closed system since kimberlite emplacement ~ 347 Ma. Complementary to insights into radiogenic isotope composition of the parental mantle source of the Udachnaya-East kimberlite, my study explores stable isotope compositions of the kimberlite groundmass (O, C and S isotopes), chloride-carbonate nodules (O and C isotopes) and two populations of olivine (O isotopes). Detailed study of zoning and composition of the groundmass olivine-II demonstrates very complex fractionation of the ultramafic primary kimberlite melt. Additional constraints are provided by olivine-hosted inclusions of cogenetic minerals, fluid and melt. The wide compositional interval shown by the cores of olivine-II (Fo86-93) reflects either crystallisation from different melt batches, or re-equilibration (in terms of Fe-Mg) with different mantle lithologies. I report the discovery of previously unknown inclusions of high-Ca pyroxene in the olivine-II cores. They formed in the diamond stability field (45-50 kb) at temperatures of 900-1100oC, from a melt with a trace element composition resembling that of the kimberlite groundmass. The inferred P-T conditions correspond to the lower part of lithosphere beneath the Siberian craton. I consider that a prolonged evolution of the kimberlite magma by olivine crystallisation was responsible for a build-up of abundances of alkalies, chloride, carbonate, and sulphate components. As a result, the residual kimberlite magma acquires an essentially non-silicate composition, but high in CO2, Cl, and alkalies. This magma crystallises at low temperatures (<650-750oC), and undergoes chloride-carbonate liquid immiscibility at ~600oC. I propose that significant amounts of alkali chlorides and carbonates in the Udachnaya-East kimberlite are pristine magmatic components inherited from the kimberlite parental/primary magma. This enrichment may be responsible for the kimberlite low liquidus temperatures, low viscosities, and rapid ascent.

No description available.

No description available.

No description available.

The estimated economic value of a stratiform mineral deposit is often very sensitive to the modelling of thickness in a conformable sequence of beds. A coregionalisation model of thickness expresses the assumed underlying spatial relationships of bedding thickness on a regional scale. Joint simulation of thickness directly models the cross-correlation of bedding thickness in such a model. Many of the current techniques of joint simulation are limited in the number of variables that can be simulated due to the multiplicative increase in processing times, based on the number of variables and number of samples simulated. To minimise processing times some methods make use of simplifying assumptions on the coregionalisation model. For example the Markov model, in which the dependence of one variable on the other is limited to the collocated data, would be unlikely to apply to the thickness of conformable bedding in a stratiform deposit. Transforming the thickness variables to remove correlation, simulating, and then back transforming to original data space offered a possible solution. The Minimum/Maximum Autocorrelation Factor (MAF) technique was chosen as one most likely to successfully decorrelate numbers of thickness variables, if the assumptions regarding a two-structure linear coregionalisation model were reasonably satisfied by the sampled data. The assumptions are that a simple intrinsic model of coregionalisation can represent both a lower correlation (‘noise’) component and a higher correlation (‘signal’) component of the modelled data. This implies that the final coregionalisation model (noise plus signal) is made up of linear combinations of a single basic structure at different spatial scales. In a number of previous applications, this had not proved to be a particularly restrictive requirement of the model. The decorrelated variables can be independently simulated, and back transformed twice; firstly using a MAF back-transformation to obtain correlated Gaussian variables, and finally to original data space. The McArthur River silver/lead/zinc stratiform deposit in the Northern Territory of Australia was chosen as the case study because it had many of the characteristics needed to test and evaluate the MAF technique in a typical stratiform deposit. The orebody model contained seventeen (17) mineralised units forming a conformable sequence which had varying thickness and degrees of mineralisation, and which had good continuity across the deposit. Cross-correlation between the thicknesses of the seventeen stratigraphic units was significant. The deposit was heavily folded in certain areas and true thickness of the bedding was calculated from drillhole log data, and used for the simulation studies. A simple unfolding algorithm was utilised to effectively flatten the deposit to allow the application of 2-D simulation techniques. Drillhole intersections often did not contain the full stratigraphic sequence of beds due to a series of normal faults criss-crossing the deposit. Therefore, incomplete data in the drillhole would need to be removed from the data set, or the number of beds in the joint simulation would need to be reduced, to utilise the MAF technique. A method was developed and validated for the generation of missing thicknesses at a sample point which removed the requirement to delete real incomplete sub-sets of the data when utilising MAF. Sequential Gaussian Simulation (SGS) was used to simulate the MAF decorrelated variables under the assumption that the multi-Gaussian assumptions held. Bedding surface simulations were generated by the addition of true thickness perpendicular to a basal reference surface. The 2-D joint simulations of thicknesses and surfaces were considered successful within a domain of the deposit where drillholes were approximately perpendicular to bedding after unfolding. The univariate, bivariate and spatial statistics of the original thickness data were reproduced accurately in the joint simulation model, including the crossvariograms of original thickness; especially compared to those obtained using independent simulation of thickness. It was concluded that the techniques could be successfully applied to other stratiform deposits if the recommended validation steps were carried out. No further difficulties should be encountered in applying the method to 2-D joint simulation of grades in a stratiform deposit. The full 3-D joint simulation of variables in any deposit using MAF would be assisted by the technique to generate missing variables at a point.

The estimated economic value of a stratiform mineral deposit is often very sensitive to the modelling of thickness in a conformable sequence of beds. A coregionalisation model of thickness expresses the assumed underlying spatial relationships of bedding thickness on a regional scale. Joint simulation of thickness directly models the cross-correlation of bedding thickness in such a model. Many of the current techniques of joint simulation are limited in the number of variables that can be simulated due to the multiplicative increase in processing times, based on the number of variables and number of samples simulated. To minimise processing times some methods make use of simplifying assumptions on the coregionalisation model. For example the Markov model, in which the dependence of one variable on the other is limited to the collocated data, would be unlikely to apply to the thickness of conformable bedding in a stratiform deposit. Transforming the thickness variables to remove correlation, simulating, and then back transforming to original data space offered a possible solution. The Minimum/Maximum Autocorrelation Factor (MAF) technique was chosen as one most likely to successfully decorrelate numbers of thickness variables, if the assumptions regarding a two-structure linear coregionalisation model were reasonably satisfied by the sampled data. The assumptions are that a simple intrinsic model of coregionalisation can represent both a lower correlation (‘noise’) component and a higher correlation (‘signal’) component of the modelled data. This implies that the final coregionalisation model (noise plus signal) is made up of linear combinations of a single basic structure at different spatial scales. In a number of previous applications, this had not proved to be a particularly restrictive requirement of the model. The decorrelated variables can be independently simulated, and back transformed twice; firstly using a MAF back-transformation to obtain correlated Gaussian variables, and finally to original data space. The McArthur River silver/lead/zinc stratiform deposit in the Northern Territory of Australia was chosen as the case study because it had many of the characteristics needed to test and evaluate the MAF technique in a typical stratiform deposit. The orebody model contained seventeen (17) mineralised units forming a conformable sequence which had varying thickness and degrees of mineralisation, and which had good continuity across the deposit. Cross-correlation between the thicknesses of the seventeen stratigraphic units was significant. The deposit was heavily folded in certain areas and true thickness of the bedding was calculated from drillhole log data, and used for the simulation studies. A simple unfolding algorithm was utilised to effectively flatten the deposit to allow the application of 2-D simulation techniques. Drillhole intersections often did not contain the full stratigraphic sequence of beds due to a series of normal faults criss-crossing the deposit. Therefore, incomplete data in the drillhole would need to be removed from the data set, or the number of beds in the joint simulation would need to be reduced, to utilise the MAF technique. A method was developed and validated for the generation of missing thicknesses at a sample point which removed the requirement to delete real incomplete sub-sets of the data when utilising MAF. Sequential Gaussian Simulation (SGS) was used to simulate the MAF decorrelated variables under the assumption that the multi-Gaussian assumptions held. Bedding surface simulations were generated by the addition of true thickness perpendicular to a basal reference surface. The 2-D joint simulations of thicknesses and surfaces were considered successful within a domain of the deposit where drillholes were approximately perpendicular to bedding after unfolding. The univariate, bivariate and spatial statistics of the original thickness data were reproduced accurately in the joint simulation model, including the crossvariograms of original thickness; especially compared to those obtained using independent simulation of thickness. It was concluded that the techniques could be successfully applied to other stratiform deposits if the recommended validation steps were carried out. No further difficulties should be encountered in applying the method to 2-D joint simulation of grades in a stratiform deposit. The full 3-D joint simulation of variables in any deposit using MAF would be assisted by the technique to generate missing variables at a point.

The estimated economic value of a stratiform mineral deposit is often very sensitive to the modelling of thickness in a conformable sequence of beds. A coregionalisation model of thickness expresses the assumed underlying spatial relationships of bedding thickness on a regional scale. Joint simulation of thickness directly models the cross-correlation of bedding thickness in such a model. Many of the current techniques of joint simulation are limited in the number of variables that can be simulated due to the multiplicative increase in processing times, based on the number of variables and number of samples simulated. To minimise processing times some methods make use of simplifying assumptions on the coregionalisation model. For example the Markov model, in which the dependence of one variable on the other is limited to the collocated data, would be unlikely to apply to the thickness of conformable bedding in a stratiform deposit. Transforming the thickness variables to remove correlation, simulating, and then back transforming to original data space offered a possible solution. The Minimum/Maximum Autocorrelation Factor (MAF) technique was chosen as one most likely to successfully decorrelate numbers of thickness variables, if the assumptions regarding a two-structure linear coregionalisation model were reasonably satisfied by the sampled data. The assumptions are that a simple intrinsic model of coregionalisation can represent both a lower correlation (‘noise’) component and a higher correlation (‘signal’) component of the modelled data. This implies that the final coregionalisation model (noise plus signal) is made up of linear combinations of a single basic structure at different spatial scales. In a number of previous applications, this had not proved to be a particularly restrictive requirement of the model. The decorrelated variables can be independently simulated, and back transformed twice; firstly using a MAF back-transformation to obtain correlated Gaussian variables, and finally to original data space. The McArthur River silver/lead/zinc stratiform deposit in the Northern Territory of Australia was chosen as the case study because it had many of the characteristics needed to test and evaluate the MAF technique in a typical stratiform deposit. The orebody model contained seventeen (17) mineralised units forming a conformable sequence which had varying thickness and degrees of mineralisation, and which had good continuity across the deposit. Cross-correlation between the thicknesses of the seventeen stratigraphic units was significant. The deposit was heavily folded in certain areas and true thickness of the bedding was calculated from drillhole log data, and used for the simulation studies. A simple unfolding algorithm was utilised to effectively flatten the deposit to allow the application of 2-D simulation techniques. Drillhole intersections often did not contain the full stratigraphic sequence of beds due to a series of normal faults criss-crossing the deposit. Therefore, incomplete data in the drillhole would need to be removed from the data set, or the number of beds in the joint simulation would need to be reduced, to utilise the MAF technique. A method was developed and validated for the generation of missing thicknesses at a sample point which removed the requirement to delete real incomplete sub-sets of the data when utilising MAF. Sequential Gaussian Simulation (SGS) was used to simulate the MAF decorrelated variables under the assumption that the multi-Gaussian assumptions held. Bedding surface simulations were generated by the addition of true thickness perpendicular to a basal reference surface. The 2-D joint simulations of thicknesses and surfaces were considered successful within a domain of the deposit where drillholes were approximately perpendicular to bedding after unfolding. The univariate, bivariate and spatial statistics of the original thickness data were reproduced accurately in the joint simulation model, including the crossvariograms of original thickness; especially compared to those obtained using independent simulation of thickness. It was concluded that the techniques could be successfully applied to other stratiform deposits if the recommended validation steps were carried out. No further difficulties should be encountered in applying the method to 2-D joint simulation of grades in a stratiform deposit. The full 3-D joint simulation of variables in any deposit using MAF would be assisted by the technique to generate missing variables at a point.

The Mudgee-Gulgong district is located within the exposed northeastern margin of the Lachlan Fold Belt in New South Wales. The district was an important gold mining centre in the 1800's and produced up to 1 million ounces of gold, mostly from deep leads. Re-mapping of the area has resulted in a major revision to the stratigraphy and structural knowledge of the area. Significant changes include the recognition of the formerly known Early Devonian Burranah Formation as a Late Ordovician volcanic unit with significant exploration potential for Au-Cu mineralization. Also recognised is a Late Silurian shelf sequence with potential for Au-Cu and base metals overlying the Burranah Formation. The Burranah Formation is a dominantly submarine, volcano-sedimentary succession with a complex internal stratigraphy. Two main lithofacies associations can be recognised on the magnetic images. A lower package, composed mostly of primary volcanic rocks and minor volcaniclastics is overlain by a package composed dominantly of volcaniclastics and sediments. Small elongate intrusive bodies occur throughout the sequence. Structural interpretation of the area reveals one dominant D2 deformation (Early Carboniferous) that produced meridional to northwest-trending folds, cleavage, thrust faults and oblique-slip faults. A zone of higher strain is developed within the Burranah Formation and is characterised by overturned, tight, F2 folds and considerable shortening. Mapping and interpretation of the area has been greatly assisted by the availability of high resolution gravity, magnetic and radiometric data. The interpretation of magnetic data has considerably enhanced the structural interpretation. Volcanic and intrusive rocks of the Burranah Formation comprise a coherent calcalkaline suite with a dominantly shoshonitic character. In MORB-normalized plots, they display patterns typical of many modern subduction-related volcanics with a marked depletion of Ta and Nb and similar or lower abundances of the heavy REE and Ti. Positive εNd values indicate a mantle source for the shoshonites with little or no crustal contamination. Primary gold mineralization in the district occurs in veins and as disseminations in the structurally more competent rocks adjacent to faults and shear zones in the higher strain zone. Host rocks are generally intrusive monzodiorites, diorites or coherent volcanics and range in age from Late Ordovician to Early Devonian. Sulphur and lead isotope data support a syndeformational model for mineralization with fluids and gold derived from the host rock sequence.

The estimated economic value of a stratiform mineral deposit is often very sensitive to the modelling of thickness in a conformable sequence of beds. A coregionalisation model of thickness expresses the assumed underlying spatial relationships of bedding thickness on a regional scale. Joint simulation of thickness directly models the cross-correlation of bedding thickness in such a model. Many of the current techniques of joint simulation are limited in the number of variables that can be simulated due to the multiplicative increase in processing times, based on the number of variables and number of samples simulated. To minimise processing times some methods make use of simplifying assumptions on the coregionalisation model. For example the Markov model, in which the dependence of one variable on the other is limited to the collocated data, would be unlikely to apply to the thickness of conformable bedding in a stratiform deposit. Transforming the thickness variables to remove correlation, simulating, and then back transforming to original data space offered a possible solution. The Minimum/Maximum Autocorrelation Factor (MAF) technique was chosen as one most likely to successfully decorrelate numbers of thickness variables, if the assumptions regarding a two-structure linear coregionalisation model were reasonably satisfied by the sampled data. The assumptions are that a simple intrinsic model of coregionalisation can represent both a lower correlation (‘noise’) component and a higher correlation (‘signal’) component of the modelled data. This implies that the final coregionalisation model (noise plus signal) is made up of linear combinations of a single basic structure at different spatial scales. In a number of previous applications, this had not proved to be a particularly restrictive requirement of the model. The decorrelated variables can be independently simulated, and back transformed twice; firstly using a MAF back-transformation to obtain correlated Gaussian variables, and finally to original data space. The McArthur River silver/lead/zinc stratiform deposit in the Northern Territory of Australia was chosen as the case study because it had many of the characteristics needed to test and evaluate the MAF technique in a typical stratiform deposit. The orebody model contained seventeen (17) mineralised units forming a conformable sequence which had varying thickness and degrees of mineralisation, and which had good continuity across the deposit. Cross-correlation between the thicknesses of the seventeen stratigraphic units was significant. The deposit was heavily folded in certain areas and true thickness of the bedding was calculated from drillhole log data, and used for the simulation studies. A simple unfolding algorithm was utilised to effectively flatten the deposit to allow the application of 2-D simulation techniques. Drillhole intersections often did not contain the full stratigraphic sequence of beds due to a series of normal faults criss-crossing the deposit. Therefore, incomplete data in the drillhole would need to be removed from the data set, or the number of beds in the joint simulation would need to be reduced, to utilise the MAF technique. A method was developed and validated for the generation of missing thicknesses at a sample point which removed the requirement to delete real incomplete sub-sets of the data when utilising MAF. Sequential Gaussian Simulation (SGS) was used to simulate the MAF decorrelated variables under the assumption that the multi-Gaussian assumptions held. Bedding surface simulations were generated by the addition of true thickness perpendicular to a basal reference surface. The 2-D joint simulations of thicknesses and surfaces were considered successful within a domain of the deposit where drillholes were approximately perpendicular to bedding after unfolding. The univariate, bivariate and spatial statistics of the original thickness data were reproduced accurately in the joint simulation model, including the crossvariograms of original thickness; especially compared to those obtained using independent simulation of thickness. It was concluded that the techniques could be successfully applied to other stratiform deposits if the recommended validation steps were carried out. No further difficulties should be encountered in applying the method to 2-D joint simulation of grades in a stratiform deposit. The full 3-D joint simulation of variables in any deposit using MAF would be assisted by the technique to generate missing variables at a point.

The active Orakeikorako-Te Kopia geothermal system was drilled in the mid-1960’s, down to 1405m, as part of a programme to investigate its electrical generation capability. Four wells were completed at Orakeikorako (23km NNE of Taupo) and two at Te Kopia, 9.5km further northeast. The exploration drilling provided information on the present day hydrological and thermal regime which is as hot as 265°C (1137m drilled depth (-801m RL) in OK-2). Major flows into the wells occurred at depths down to 850m, although poor permeability and decline in mass output discouraged development. The waters discharged were of near neutral pH and had low salinities (highest Cl content from OK-2 ≈546mg/kg), low discharge enthalpies and indicated water temperatures (TSiO2 and TNaKCa) of 2l0°C to 240°C. A hydrologic model proposed here envisages a hot water reservoir in the OK-2 area (northeastern part of the Orakeikorako thermal area) with a lateral flow supplying water to the Red Hill (OK-4 area) in the southern part of the system and a concealed northeast flow which reaches the surface at Te Kopia. The Orakeikorako thermal area occupies a surface area of about 1.8km2, mainly on the east bank of the Waikato River, where dilute chloride-bicarbonate water discharges along faults and fractures in association with an extensive silica sinter sheet, boiling springs and geysers. The occurrence of a mordenite-smectite assemblage at shallow depths, plus the oxygen and hydrogen isotopic composition of surface discharge waters, indicate that the ascending chloride fluids are diluted by near surface (heated?) groundwaters. The δD shift from local groundwater composition may be evidence for a magmatic component to the convecting hydrothermal system. Incursion of fluids from the relatively cool (<l20°C) steam-heated carapace into deep levels of the system and its mixing with the alkali-chloride fluids, produces argillic alteration, sealing and will eventually result in the demise of the system. Old silica sinter on the west bank, at the foot of the Tutukau Rhyolite Dome, is covered by Oruanui Ash (22,700 years B.P.) and demonstrates that the hydrologic character of this part of the system has changed due to a combination of fault movement, changes in the height of the watertable and sealing. The Te Kopia thermal area is located along 2.5km of the Paeroa Fault scarp, a major structural feature inferred to be controlling migration of deep hydrothermal fluids in the Orakeikorako-Te Kopia area. Surface activity at Te Kopia is characterised by acid alteration (including fumaroles, warm acid pools and steaming ground), although neutral pH alkali-chloride fluids discharged here within the last 3000 years and deposited silica sinter (C14 age on wood enveloped by sinter is 3026 +/- 43years B.P.). New thermal areas in the past --year have begun to develop in the northwestern part of Te Kopia, whilst cold hydrothermally altered ground (hosting a mordenite + clay assemblage) records a decline in activity in the southern part of the Te Kopia thermal area. The system is hosted by a generally SE dipping sequence of Pliocene to Quaternary ignimbrite, tuff and rhyolite lavas of the Taupo Volcanic Zone. Point counting, electron microprobe analyses of surviving primary phases (Fe, Mg, Al and Ti contents of hornblende and biotite), together with X-ray fluorescence and neutron activation analysis were used to distinguish three extensive ignimbrites encountered in the Orakeikorako-Te Kopia drillholes: (0.33Ma, sanidine-bearing) Paeroa, (0.35Ma) Te Kopia and (undated) Akatarewa Ignimbrites, despite their having been hydrothermally altered. Ignimbrite recognition is made on the basis of a combination of immobile trace and rare earth element abundances and ratios: Ta and Yb (ppm), P2O5(%) and the ratios Zr/Yb, Zr/Y, Yb/Hf, La/Lu, Nb/Hf, Zr/Nb, Zr/Lu, Yb/Ta, Ta/Lu, La/Tb and Nb/Ta. The Paeroa Ignimbrite is distinguished by is Eu anomaly ((Eu/Eu*)cn is 0.48 to 0.54), whereas the Te Kopia and Akatarewa Ignimbrites are characterised by their flatter REE Spidergrams ((Eu/Eu*)cn is ~1.0 and ~0.8 respectively). The correlation of the extensive ignimbrites was satisfactorily effected by a combination of their characteristic bulk rock and pumice chemistry, plus primary mineralogy, to enable the subsurface stratigraphy and structure of the Orakeikorako-Te Kopia geothermal system to be defined. The alteration assemblage below 500m consists of quartz, albite+adularia, with variable abundence and distribution of chlorite, pyrite, calcite, wairakite, epidote, pyrrhotite, titanite, leucoxene, siderite and clinozoisite; illite is a late overprint. Rare almandine occurs in rhyolite in OK-1: 1312.5m; this is the first known occurrence of garnet in an active geothermal system of the TVZ. The surficial alteration assemblage of kaolin, cristobalite, alunite, hematite and jarosite reflects alteration by acid sulphate-steam heated waters. The occurrence and textual relations exhibited by the hydrothermal mineral assemblage define the geochemical structure and thermal evolution of the Orakeikorako-Te Kopia system The activities of components of minerals, determined from electron microprobe analyses and composition-activity relationships (OK-2 discharge: logαK+/αH+=3.6, logαNa+/αH+=4.8) support the petrologic observation that illite is now the stable potassium phase (overprinting adularia), although a state of equilibrium between the sheet silicate and the fluids is clearly not fully reached. The Na/K ratio of the altering fluid is controlled by the albite-adularia reaction (dissolution of albite and replacement by adularia, after andesine), whilst the H2/H2S ratio is buffered by the virtually complete replacement of pyrrhotite by pyrite. The fluids are now slightly undersaturated with respect to calcite, this is shown by etched surfaces on some calcite grains. In the past the deep fluid boiled adiabatically from >300°C to ~250°C as it ascended, resulting in the deposition of adularia, quartz and bladed calcite. The system has cooled, resulting in lower subsurface temperatures (as recorded by fluid inclusion geothermometry) suppressing boiling, and migrated northwards as a consequence of self sealing. The thermal decline and retention of CO2 in the deep alkali-chloride fluid shifted the alteration assemblage from one of albite-adularia stability to illite stability. The homogenisation (Th) temperatures of primary and secondary liquid-rich inclusions in 27 cores from different depths mostly match measured temperature profiles (e.g. OK-1 (shallow levels) and OK-2). Never-the-less, fluid inclusion data support mineral-inferred stability temperatures which indicate that parts of the Orakeikorako-Te Kopia system have cooled appreciably (e.g. OK-1, deep levels) and OK-4 (maximum Tbore=238°C, maximum Th=312°C; epidote abundant). In contrast, the northwestern margin (OK-6 area) has heated (OK-6:1113.4m; Tbore=261°C, Th=210-221°C). Some inclusions in the Te Kopia drillholes have Th values that exceed Tbore by as much as 50°C, and are deduced to have been uplifted by movement on the Paeroa Fault. Freezing data indicate that the trapped fluid was dilute (~0.2 to 1.7 wt% NaCl equivalent) since most Tm values range from -0.1 to -0.5°C. The outflow portion of the Orakeikorako-Te Kopia system has evolved recently, both chemically and physically. Movement on the Paeroa Fault, that uplifted pyroclastic rocks hosting a quartz-adularia-illite assemblage, combined with a lowering of the watertable has resulted in an overprinting of the neutral pH hydrothermal mineral assemblage by a kaolinite-alunite type assemblage which derives from an acid sulphate fluid. Quartz crystals found 150m above the base of the Paeroa Fault scarp host dilute (~1.5wt% NaCl equivalent) fluid inclusions with Th values that range from 180-206°C (average 196°C). Bladed quartz (after calcite) did not contain usable inclusions. It is deduced that the inclusions formed about 120-160m below the ground, which indicates uplift in the order of ~300m. Assuming a constant rate of uplift of 4m/ka (based on the offset of 330ka Paeroa Ignimbrite), the minimum duration of activity at Te Kopia is 75,000 years.