Sarah D Milicich - Academia.edu (original) (raw)

Papers by Sarah D Milicich

Journal of Volcanology and Geothermal Research

GSA Bulletin

Hydrothermal eruptions are the most violent and hazardous phenomena within geothermal fields. The... more Hydrothermal eruptions are the most violent and hazardous phenomena within geothermal fields. The largest of these may produce kilometer-sized craters and breccia deposits that are tens of meters thick. The geological and hydrothermal priming that leads to these types of eruptions is poorly understood. To understand large hydrothermal eruptions, we investigated a series of prehistoric events at the Rotokawa geothermal field in New Zealand. By revising the stratigraphy and distribution of hydrothermal breccia deposits and correlating these with componentry, crater morphology, and subsurface geological structure, we estimated the frequency, priming processes, triggers, and dynamics of multiple eruptions. Seventeen large hydrothermal eruptions occurred centuries to millennia apart in the period from ca. 22 cal ka B.P. to ca. 3.4 cal ka B.P. Of six hydrothermal eruptions since ca. 7 ka, four produced oval-shaped craters up to 2 km in diameter, creating a broad, shallow depression within...

Fingerprinting the temperature and fluid source of fracture-filling calcite in geothermal systems... more Fingerprinting the temperature and fluid source of fracture-filling calcite in geothermal systems using clumped isotopes JOHN MACDONALD, SARAH MILICICH, AMELIA DAVIES, CHRIS HOLDSWORTH, MICHAEL NEWTON, SAM WILLIAMSON, JOHN FAITHFULL, DAVID MCNAMARA, CEDRIC JOHN School of Geographical and Earth Sciences, University of Glasgow, john.macdonald.3@glasgow.ac.uk Geothermal Energy, GNS Science Carbonate Research, Department of Earth Science and Engineering, Imperial College London Hunterian Museum, University of Glasgow Department of Earth and Ocean Sciences, NUI Galway

Economic Geology

Downhole data and cores collected during International Ocean Discovery Program (IODP) Expedition ... more Downhole data and cores collected during International Ocean Discovery Program (IODP) Expedition 376 at Brothers volcano, Kermadec arc, provide unprecedented, in situ views of volcanic facies and fluid pathways in an actively forming volcanogenic massive sulfide (VMS) ore deposit. Brothers volcano is a submarine caldera with extensive sea floor hydrothermal alteration. Downhole data were collected in two holes: Hole U1530A at the NW Caldera and Hole U1528D at the Upper Cone. Textural analysis of microresistivity images in Hole U1530A provides a continuous image facies record that greatly improves findings based upon sporadic and partial (18%) core recovery. Between 90 and 214 meters below sea floor (mbsf), the heterogeneous image facies with local pattern variations is consistent with the volcaniclastic facies interpreted from cores. Between 232 and 445 mbsf, a volcanic facies was not recognizable in cores because of overprinting alteration, apart from five intervals of coherent lav...

This study is part of GNS Science’s New Zealand Geothermal Future research programme, funding of ... more This study is part of GNS Science’s New Zealand Geothermal Future research programme, funding of which was provided by the Government of New Zealand. We thank Contact Energy Ltd. for the provision and permission to publish well data. The authors acknowledge support of this work by Haliburton Software and Services, a Haliburton Company, through the use of RecallTM Borehole software. Thanks to Fabian Sepulveda, Mark Lawrence, and Michael Rosenberg for valuable discussion and editorial comments.

A more detailed understanding of the Rotokawa geothermal system, central Taupō Volcanic Zone (New... more A more detailed understanding of the Rotokawa geothermal system, central Taupō Volcanic Zone (New Zealand), has been realised in order to constrain the magmatic, volcanic, structural and hydrothermal evolution of the hottest utilised geothermal system of New Zealand. Geochronology undertaken on buried hydrothermally altered lithologies at Rotokawa has provided constraints on the stratigraphy and volcanic evolution of the region. A 3-km-thick sequence of volcanic products is present at Rotokawa. This sequence is comprised of rhyolitic ignimbrites from large, caldera-forming events at volcanoes outside the field area, and locally sourced andesite and rhyolite lava bodies. The oldest volcanic rock from U-Pb dating of zircon is an ignimbrite, which yields an eruption age estimate of 1.84 ± 0.04 Ma. This ignimbrite, part of the Tahorakuri Formation, is among the oldest silicic volcanic deposits from the Taupō Volcanic Zone and can be linked to comparably-aged counterparts at three other ...

The Taupo Volcanic Zone (TVZ), located in the central North Island of New Zealand, is an actively... more The Taupo Volcanic Zone (TVZ), located in the central North Island of New Zealand, is an actively rifting volcanic arc. Heat flux in the central part of the TVZ is exceptionally high (700 mW/m), and is focussed at the surface through 23 high-temperature geothermal systems. Many of these systems are closely spaced (~5-7 km) with some appearing to align parallel to the eastern TVZ rift margin, while others appear more randomly located. Understanding what controls the locations of the geothermal systems is important to determine whether systems are connected and interacting at depth, to identify where blind systems might be, and to understand how heat output might change over time. Numerical fluid flow models allow us to test how the locations of geothermal systems are influenced by variables such as rock properties, heat and fluid sources, and faulting. For a region within the TVZ, we have created simplified models and individually varied surface recharge, lithology, permeability, and...

Structures such as fractures and faults have an important role as fluid flow pathways in geotherm... more Structures such as fractures and faults have an important role as fluid flow pathways in geothermal fields, as the reservoir rocks hosting geothermal resources can often have little to no intrinsic permeability. As such, understanding and characterizing this structural network is vital to developing reservoir models and field operation and development plans that will maximize the potential of a geothermal resource. Presented here are the preliminary results of three recent studies, micro-earthquake analysis, borehole logging, and active fault mapping, carried out in the Wairakei Geothermal Field to determine the structural character of the system, if and how it contributes to fluid flow, and how the structural observations from these studies inform and relate to each other. Across all three techniques a dominant NE-SW structure strike orientation is observed with lesser population of N-S, E-W and NW-SE, consistent with the broad Taupo Volcanic Zone observed trend. Further analysis o...

This study is part of a contribution from GNS Science’s Geothermal Resources of New Zealand and N... more This study is part of a contribution from GNS Science’s Geothermal Resources of New Zealand and New Zealand Geothermal Future research programmes, funding of which was provided by the Government of New Zealand. We thank Contact Energy Ltd for the provision and permission to publish well data. The authors acknowledge support of this work by Haliburton Software and Services, a Haliburton Company, through the use of RecallTM Borehole software.

INTERACTION: INTeraction between lifE, Rifting And Caldera Tectonics In OkataiNa Cécile Massiot1,... more INTERACTION: INTeraction between lifE, Rifting And Caldera Tectonics In OkataiNa Cécile Massiot1, Craig Miller2, Matthew Stott3, Pilar Villamor1, Hiroshi Asanuma4, Eric Boyd5, Matteo Lelli 6 , David D. Mcnamara 7 , Santanu Misra 8 , Doug R. Schmitt 9 , Guido Ventura 10 , Pujun Wang 11 , Ludmila Adam 12 , Edward Bertrand 1 , Fabio Caratori Tontini 1 , Geoff Kilgour 2 , Sarah D. Milicich 1 , Alex Nichols 13 , and Francesco Parisio 14

Diagrammatic 2D representation (i.e., cross-sections and maps) of drillhole data (e.g. stratigrap... more Diagrammatic 2D representation (i.e., cross-sections and maps) of drillhole data (e.g. stratigraphy, permeable zones, secondary mineral occurrence) and inferences (e.g. hydrology, structural relations) have historically been used for visualisation. Advances have been made using newly developed 3D computer modeling software where we are able to render detailed geological information (e.g., stratigraphy, structure, hydrothermal alteration mineralogy) and overlay it with hydrological data (e.g., temperature, flow data). This provides greater insights into active fluid flow behaviour in the geothermal reservoir, and the thermal and chemical evolution of the geothermal system, leading to greater efficiency in the decision-making processes at all stages of field exploration, reservoir development and production. “Earth Research” is 3D modelling software that has been developed by ARANZ (a New Zealand-based software development company), with scientific input from GNS Science and Contact E...

Active faults in rifts commonly provide high crustal permeability and control geothermal fluid pa... more Active faults in rifts commonly provide high crustal permeability and control geothermal fluid pathways. However, active faults can also pose surface deformation hazards to geothermal power plants and associated infrastructure. The New Zealand Ministry for the Environment (MfE) guidelines recommend avoidance of active faults for construction of new buildings based on building importance and the rate of fault activity. Power plants, which are classed as 'high Building Importance Category', are permitted on faults with a rupture recurrence interval greater than 10,000 years. We present a site feasibility study for the Te Mihi Power Plant (Wairakei Geothermal Field), used to determine if there is recent major active faulting at the proposed site. The initial Power Plant site was proposed in an area exhibiting complex surface patterns of active faults with two closely spaced (few metres to hundreds of metres), intersecting, normal fault sets. Detailed aerial photo review and fie...

The value of information that can be gleaned from hydrothermal mineral studies in geothermal expl... more The value of information that can be gleaned from hydrothermal mineral studies in geothermal exploration and development projects is well known. Identification and interpretation of hydrothermal mineral assemblages is an important aspect of surface and subsurface geothermal exploration, as it may provide insight into the present and/or past nature of the geothermal reservoir. Observational and analytical tools available to the exploration geothermal geologist are wide and increasingly sophisticated. For several decades, the significance of mineral occurrences (e.g., indicators of temperature conditions at the time of mineral formation), textural relations (e.g., insights into system longevity and evolution, or influx of cool marginal fluid ingress) and chemistry (e.g., indicators of low pH conditions, potential for natural self-sealing or development-induced scaling etc.) has been recognised. However, at a time of geothermal renaissance in many parts of the World, it is a concern th...

Discerning the contributions to fluid flow in a geothermal reservoir from intrinsic and structura... more Discerning the contributions to fluid flow in a geothermal reservoir from intrinsic and structural permeability components is an important, yet difficult task. High-quality, resistivity borehole image log data (Formation MicroImager; FMI) collected from the Whakamaru Group ignimbrite in well WK271, Wairakei Geothermal Field, New Zealand, has been used to investigate the textural characteristics of volcanic rocks in the geothermal reservoir, with a view to improving reservoir model inputs. Textural analysis of the FMI log in the Whakamaru Group ignimbrite was able to provide an improved internal stratigraphy compared to that derived solely from drill-cuttings, and offers insights into the volcanic processes that generated it. Based on volcanic textures identified on the WK271 FMI image log, seven individual flow units in the Whakamaru Group ignimbrite are recognized, and are separated by texturally characteristic intervals of airfall tephra. Comparison of fracture density and rock ty...

In the last 4 years to mid 2009, more than 45 geothermal wells (i.e., production, shallow ( 400 m... more In the last 4 years to mid 2009, more than 45 geothermal wells (i.e., production, shallow ( 400 m deeper at Wairakei (below -2250 mRSL) than previously believed, whereas it has now been encountered by deep drilling (in TH17) from -1484 mRSL in the NE sector of Tauhara. Interpretation of recent drilling results by GNS Science, complemented by detailed petrology, provide a geological framework for identifying future drilling targets. Whilst fault zones provide up-flow channels, we now appreciate intra- and inter-formational permeable zones provide major inflows to the production wells, and an important control on lateral fluid flow at Wairakei and Tauhara. Hydrothermal mineral studies confirm a prograde trend in alteration rank and intensity with depth, and point to thermal and chemical change in the western Wairakei-Tauhara system that has created a lower temperature mineral overprint of the early propylitic assemblage, whilst conditions at the eastern boundary of the system have lon...

The development and management of high-temperature geothermal resources for electrical power gene... more The development and management of high-temperature geothermal resources for electrical power generation requires accurate knowledge of the local geological conditions, particularly where they impact on the hydrology of the resource. This study is an integrated programme of work designed to develop new perspectives on the geological and structural framework of the Kawerau geothermal resource as a sound basis for field management. Although the geological approaches and techniques utilised in this study have previously been used, their application to an integrated study of a geothermal system in New Zealand has not been previously undertaken. Correlating volcanic and sedimentary stratigraphy in geothermal areas in New Zealand can be challenging due to similarities in lithology and the destruction of distinctive chemical, mineralogical and textural characteristic by hydrothermal alteration. A means to overcoming these issues is to utilise dating to correlate the stratigraphy. Zircons a...

Journal of Volcanology and Geothermal Research

GSA Bulletin

Hydrothermal eruptions are the most violent and hazardous phenomena within geothermal fields. The... more Hydrothermal eruptions are the most violent and hazardous phenomena within geothermal fields. The largest of these may produce kilometer-sized craters and breccia deposits that are tens of meters thick. The geological and hydrothermal priming that leads to these types of eruptions is poorly understood. To understand large hydrothermal eruptions, we investigated a series of prehistoric events at the Rotokawa geothermal field in New Zealand. By revising the stratigraphy and distribution of hydrothermal breccia deposits and correlating these with componentry, crater morphology, and subsurface geological structure, we estimated the frequency, priming processes, triggers, and dynamics of multiple eruptions. Seventeen large hydrothermal eruptions occurred centuries to millennia apart in the period from ca. 22 cal ka B.P. to ca. 3.4 cal ka B.P. Of six hydrothermal eruptions since ca. 7 ka, four produced oval-shaped craters up to 2 km in diameter, creating a broad, shallow depression within...

Fingerprinting the temperature and fluid source of fracture-filling calcite in geothermal systems... more Fingerprinting the temperature and fluid source of fracture-filling calcite in geothermal systems using clumped isotopes JOHN MACDONALD, SARAH MILICICH, AMELIA DAVIES, CHRIS HOLDSWORTH, MICHAEL NEWTON, SAM WILLIAMSON, JOHN FAITHFULL, DAVID MCNAMARA, CEDRIC JOHN School of Geographical and Earth Sciences, University of Glasgow, john.macdonald.3@glasgow.ac.uk Geothermal Energy, GNS Science Carbonate Research, Department of Earth Science and Engineering, Imperial College London Hunterian Museum, University of Glasgow Department of Earth and Ocean Sciences, NUI Galway

Economic Geology

Downhole data and cores collected during International Ocean Discovery Program (IODP) Expedition ... more Downhole data and cores collected during International Ocean Discovery Program (IODP) Expedition 376 at Brothers volcano, Kermadec arc, provide unprecedented, in situ views of volcanic facies and fluid pathways in an actively forming volcanogenic massive sulfide (VMS) ore deposit. Brothers volcano is a submarine caldera with extensive sea floor hydrothermal alteration. Downhole data were collected in two holes: Hole U1530A at the NW Caldera and Hole U1528D at the Upper Cone. Textural analysis of microresistivity images in Hole U1530A provides a continuous image facies record that greatly improves findings based upon sporadic and partial (18%) core recovery. Between 90 and 214 meters below sea floor (mbsf), the heterogeneous image facies with local pattern variations is consistent with the volcaniclastic facies interpreted from cores. Between 232 and 445 mbsf, a volcanic facies was not recognizable in cores because of overprinting alteration, apart from five intervals of coherent lav...

This study is part of GNS Science’s New Zealand Geothermal Future research programme, funding of ... more This study is part of GNS Science’s New Zealand Geothermal Future research programme, funding of which was provided by the Government of New Zealand. We thank Contact Energy Ltd. for the provision and permission to publish well data. The authors acknowledge support of this work by Haliburton Software and Services, a Haliburton Company, through the use of RecallTM Borehole software. Thanks to Fabian Sepulveda, Mark Lawrence, and Michael Rosenberg for valuable discussion and editorial comments.

A more detailed understanding of the Rotokawa geothermal system, central Taupō Volcanic Zone (New... more A more detailed understanding of the Rotokawa geothermal system, central Taupō Volcanic Zone (New Zealand), has been realised in order to constrain the magmatic, volcanic, structural and hydrothermal evolution of the hottest utilised geothermal system of New Zealand. Geochronology undertaken on buried hydrothermally altered lithologies at Rotokawa has provided constraints on the stratigraphy and volcanic evolution of the region. A 3-km-thick sequence of volcanic products is present at Rotokawa. This sequence is comprised of rhyolitic ignimbrites from large, caldera-forming events at volcanoes outside the field area, and locally sourced andesite and rhyolite lava bodies. The oldest volcanic rock from U-Pb dating of zircon is an ignimbrite, which yields an eruption age estimate of 1.84 ± 0.04 Ma. This ignimbrite, part of the Tahorakuri Formation, is among the oldest silicic volcanic deposits from the Taupō Volcanic Zone and can be linked to comparably-aged counterparts at three other ...

The Taupo Volcanic Zone (TVZ), located in the central North Island of New Zealand, is an actively... more The Taupo Volcanic Zone (TVZ), located in the central North Island of New Zealand, is an actively rifting volcanic arc. Heat flux in the central part of the TVZ is exceptionally high (700 mW/m), and is focussed at the surface through 23 high-temperature geothermal systems. Many of these systems are closely spaced (~5-7 km) with some appearing to align parallel to the eastern TVZ rift margin, while others appear more randomly located. Understanding what controls the locations of the geothermal systems is important to determine whether systems are connected and interacting at depth, to identify where blind systems might be, and to understand how heat output might change over time. Numerical fluid flow models allow us to test how the locations of geothermal systems are influenced by variables such as rock properties, heat and fluid sources, and faulting. For a region within the TVZ, we have created simplified models and individually varied surface recharge, lithology, permeability, and...

Structures such as fractures and faults have an important role as fluid flow pathways in geotherm... more Structures such as fractures and faults have an important role as fluid flow pathways in geothermal fields, as the reservoir rocks hosting geothermal resources can often have little to no intrinsic permeability. As such, understanding and characterizing this structural network is vital to developing reservoir models and field operation and development plans that will maximize the potential of a geothermal resource. Presented here are the preliminary results of three recent studies, micro-earthquake analysis, borehole logging, and active fault mapping, carried out in the Wairakei Geothermal Field to determine the structural character of the system, if and how it contributes to fluid flow, and how the structural observations from these studies inform and relate to each other. Across all three techniques a dominant NE-SW structure strike orientation is observed with lesser population of N-S, E-W and NW-SE, consistent with the broad Taupo Volcanic Zone observed trend. Further analysis o...

This study is part of a contribution from GNS Science’s Geothermal Resources of New Zealand and N... more This study is part of a contribution from GNS Science’s Geothermal Resources of New Zealand and New Zealand Geothermal Future research programmes, funding of which was provided by the Government of New Zealand. We thank Contact Energy Ltd for the provision and permission to publish well data. The authors acknowledge support of this work by Haliburton Software and Services, a Haliburton Company, through the use of RecallTM Borehole software.

INTERACTION: INTeraction between lifE, Rifting And Caldera Tectonics In OkataiNa Cécile Massiot1,... more INTERACTION: INTeraction between lifE, Rifting And Caldera Tectonics In OkataiNa Cécile Massiot1, Craig Miller2, Matthew Stott3, Pilar Villamor1, Hiroshi Asanuma4, Eric Boyd5, Matteo Lelli 6 , David D. Mcnamara 7 , Santanu Misra 8 , Doug R. Schmitt 9 , Guido Ventura 10 , Pujun Wang 11 , Ludmila Adam 12 , Edward Bertrand 1 , Fabio Caratori Tontini 1 , Geoff Kilgour 2 , Sarah D. Milicich 1 , Alex Nichols 13 , and Francesco Parisio 14

Diagrammatic 2D representation (i.e., cross-sections and maps) of drillhole data (e.g. stratigrap... more Diagrammatic 2D representation (i.e., cross-sections and maps) of drillhole data (e.g. stratigraphy, permeable zones, secondary mineral occurrence) and inferences (e.g. hydrology, structural relations) have historically been used for visualisation. Advances have been made using newly developed 3D computer modeling software where we are able to render detailed geological information (e.g., stratigraphy, structure, hydrothermal alteration mineralogy) and overlay it with hydrological data (e.g., temperature, flow data). This provides greater insights into active fluid flow behaviour in the geothermal reservoir, and the thermal and chemical evolution of the geothermal system, leading to greater efficiency in the decision-making processes at all stages of field exploration, reservoir development and production. “Earth Research” is 3D modelling software that has been developed by ARANZ (a New Zealand-based software development company), with scientific input from GNS Science and Contact E...

Active faults in rifts commonly provide high crustal permeability and control geothermal fluid pa... more Active faults in rifts commonly provide high crustal permeability and control geothermal fluid pathways. However, active faults can also pose surface deformation hazards to geothermal power plants and associated infrastructure. The New Zealand Ministry for the Environment (MfE) guidelines recommend avoidance of active faults for construction of new buildings based on building importance and the rate of fault activity. Power plants, which are classed as 'high Building Importance Category', are permitted on faults with a rupture recurrence interval greater than 10,000 years. We present a site feasibility study for the Te Mihi Power Plant (Wairakei Geothermal Field), used to determine if there is recent major active faulting at the proposed site. The initial Power Plant site was proposed in an area exhibiting complex surface patterns of active faults with two closely spaced (few metres to hundreds of metres), intersecting, normal fault sets. Detailed aerial photo review and fie...

The value of information that can be gleaned from hydrothermal mineral studies in geothermal expl... more The value of information that can be gleaned from hydrothermal mineral studies in geothermal exploration and development projects is well known. Identification and interpretation of hydrothermal mineral assemblages is an important aspect of surface and subsurface geothermal exploration, as it may provide insight into the present and/or past nature of the geothermal reservoir. Observational and analytical tools available to the exploration geothermal geologist are wide and increasingly sophisticated. For several decades, the significance of mineral occurrences (e.g., indicators of temperature conditions at the time of mineral formation), textural relations (e.g., insights into system longevity and evolution, or influx of cool marginal fluid ingress) and chemistry (e.g., indicators of low pH conditions, potential for natural self-sealing or development-induced scaling etc.) has been recognised. However, at a time of geothermal renaissance in many parts of the World, it is a concern th...

Discerning the contributions to fluid flow in a geothermal reservoir from intrinsic and structura... more Discerning the contributions to fluid flow in a geothermal reservoir from intrinsic and structural permeability components is an important, yet difficult task. High-quality, resistivity borehole image log data (Formation MicroImager; FMI) collected from the Whakamaru Group ignimbrite in well WK271, Wairakei Geothermal Field, New Zealand, has been used to investigate the textural characteristics of volcanic rocks in the geothermal reservoir, with a view to improving reservoir model inputs. Textural analysis of the FMI log in the Whakamaru Group ignimbrite was able to provide an improved internal stratigraphy compared to that derived solely from drill-cuttings, and offers insights into the volcanic processes that generated it. Based on volcanic textures identified on the WK271 FMI image log, seven individual flow units in the Whakamaru Group ignimbrite are recognized, and are separated by texturally characteristic intervals of airfall tephra. Comparison of fracture density and rock ty...

In the last 4 years to mid 2009, more than 45 geothermal wells (i.e., production, shallow ( 400 m... more In the last 4 years to mid 2009, more than 45 geothermal wells (i.e., production, shallow ( 400 m deeper at Wairakei (below -2250 mRSL) than previously believed, whereas it has now been encountered by deep drilling (in TH17) from -1484 mRSL in the NE sector of Tauhara. Interpretation of recent drilling results by GNS Science, complemented by detailed petrology, provide a geological framework for identifying future drilling targets. Whilst fault zones provide up-flow channels, we now appreciate intra- and inter-formational permeable zones provide major inflows to the production wells, and an important control on lateral fluid flow at Wairakei and Tauhara. Hydrothermal mineral studies confirm a prograde trend in alteration rank and intensity with depth, and point to thermal and chemical change in the western Wairakei-Tauhara system that has created a lower temperature mineral overprint of the early propylitic assemblage, whilst conditions at the eastern boundary of the system have lon...

The development and management of high-temperature geothermal resources for electrical power gene... more The development and management of high-temperature geothermal resources for electrical power generation requires accurate knowledge of the local geological conditions, particularly where they impact on the hydrology of the resource. This study is an integrated programme of work designed to develop new perspectives on the geological and structural framework of the Kawerau geothermal resource as a sound basis for field management. Although the geological approaches and techniques utilised in this study have previously been used, their application to an integrated study of a geothermal system in New Zealand has not been previously undertaken. Correlating volcanic and sedimentary stratigraphy in geothermal areas in New Zealand can be challenging due to similarities in lithology and the destruction of distinctive chemical, mineralogical and textural characteristic by hydrothermal alteration. A means to overcoming these issues is to utilise dating to correlate the stratigraphy. Zircons a...