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Papers by Dan Jiricka

The Canadian Mineralogist, 2016

Unconformity-type uranium deposits from the Athabasca Basin area are considered to be the result ... more Unconformity-type uranium deposits from the Athabasca Basin area are considered to be the result of mixing between oxidized basinal brines and basement-derived reduced fluids/gases, and/or reduced basement rocks. Graphite and its breakdown products are suggested to be responsible for uranium mineralization by acting as a reductant that could trigger deposition of uranium. In addition, the presence of well-connected graphite and sulfides within graphitic pelitic rocks is considered to be potentially indicative of basement structures, as the minerals are often concentrated along the structures, which hence become electromagnetic (EM) conductors. Thus, exploration for uranium deposits is often focused on the search for EM conductors. Variably graphitic pelitic schists with a steeply dipping fabric underlie the sedimentary rocks of the basin in the Dufferin Lake zone, south-central Athabasca Basin (Saskatchewan, Canada). Up dip, and just below the unconformity with the Athabasca Group, the pelitic schists are replaced by texturally similar rocks within ''graphite-depleted zones''. These zones consist of chlorite and hematite alteration (Red/Green Zone; RGZ) and a bleached zone immediately adjacent to the unconformity. Both zones are characterized by a lower concentration of carbon and sulfur, with the bleached zone showing higher concentrations of uranium and boron, the latter corresponding to a high dravite content. The major elements composition of the graphite-bearing pelitic schists and altered equivalents (RGZ) are similar. Raman analyses indicate that well-ordered carbon species (graphite to semi-graphite) are present in the pelitic schists, with both types more common within shear zones. In contrast, only rare low-ordered carbon species (carbonaceous matter) were detected in the graphite-depleted samples within the RGZ. This variation is interpreted to be the result of graphite consumption by oxidizing fluids migrating downward from the Athabasca Group. This graphite consumption may have resulted in the production of a mobile reductant (gas or fluid), which may have played a subsequent role in the deposition of uranium mineralization.

Mineralium Deposita, 2016

Mineralium Deposita, 2015

The Athabasca Basin (Canada) contains the highest grade unconformity-type uranium deposits in the... more The Athabasca Basin (Canada) contains the highest grade unconformity-type uranium deposits in the world. Underlying the Athabasca Group sedimentary rocks of the Dufferin Lake Zone are variably graphitic, pelitic schists (VGPS), altered to chlorite and hematite (Red/Green Zone: RGZ). They were locally bleached near the unconformity during paleoweathering and/or later fluid interaction. Overall, graphite was lost from the RGZ and the bleached zone relative to the original VGPS. Fluid inclusions were examined in different generations of quartz veins, using microthermometry and Raman spectroscopy, to characterize and compare the different fluids that interacted with the RGZ and the VGPS. In the VGPS, CH4-, and N2-rich fluid inclusions, which homogenize into the vapor phase between −100 and −74 °C, and −152 and −125 °C, respectively, and CO2-rich fluid inclusions, homogenizing either into vapor or liquid between 20 and 28 °C, are present. Carbonic fluids could be the result of the breakdown of graphite to CH4 + CO2, whereas N2-rich fluid is interpreted to be the result of breakdown of feldspars/micas to NH4++N2. In the RGZ, the presence of fluid inclusions with low ice melting temperature (−38 to −16 °C) reflect the presence of CaCl2, and fluid inclusions with halite daughter minerals that dissolve between 190 and 240 °C indicate the presence of highly saline fluids. These fluids are interpreted to be derived from the Athabasca Basin. The circulation of carbonic fluids and brines occurred during two different events related to different P-T conditions of trapping. The carbonic fluids interacted with basement rocks during retrograde metamorphism of the basement rocks before deposition of the Athabasca Basin, whereas the brines circulated after the deposition of the Athabasca Basin. These latter fluids are similar to brines related to uranium mineralization at McArthur River and thus, in addition to possibly being related to graphite depletion in the RGZ, they could be linked to uranium mineralization.

Unconformity-type uranium deposits from the Athabasca Basin are considered to be the result of mi... more Unconformity-type uranium deposits from the Athabasca Basin are considered to be the result of mixing between oxidized basinal brines and basement-derived reduced fluids/gases, and/or reduced basement rocks. Graphite and/or its breakdown products are suggested to be responsible for uranium mineralization by acting as a reductant that could trigger deposition of uranium. Also, graphite is considered to be indicative of basement structures; being often concentrated along structures which can be identified as electromagnetic (EM) conductors. Thus, exploration for uranium deposits is often focused on the search for EM conductors. Underlying the sedimentary rocks of the basin in the Dufferin Lake zone are variably graphitic pelitic schists (VGPS); altered to chlorite and hematite (Red/Green Zone: RGZ), and locally bleached equivalents near the unconformity during paleoweathering or later fluid interactions. These altered zones are texturally similar rocks within "graphite-depleted zones" as the unconformity is approached. Both zones are characterized by a lower concentration of carbon and sulfur, with the bleached zone showing higher concentrations of uranium and boron, the latter corresponding to high dravite content. The major element composition of the graphitebearing pelitic schists and altered equivalents (RGZ) are similar. Raman analyses indicate that well-ordered carbon species (graphite to semi-graphite) are present in the pelitic schists, with both types more common within shear zones. In contrast, only rare low-ordered carbon species (carbonaceous matter) were detected in the graphite-depleted samples within the RGZ. This variation is interpreted to be the result of graphite consumption by oxidizing fluids migrating downward from the Athabasca Group. This graphite consumption may have resulted in the production of a mobile reductant (gas or fluid), which may have played a subsequent role in the deposition of uranium mineralization.

Summary The Centennial deposit represents the first discovery of high-grade unconformity-related ... more Summary The Centennial deposit represents the first discovery of high-grade unconformity-related uranium mineralization in the south-central portion of the Athabasca Basin. The deposit shares similarities to those in the eastern end of the basin, but also contains ...

Economic Geology, 2012

The Centennial U deposit is situated in the south-central Athabasca Basin (Canada) and straddles ... more The Centennial U deposit is situated in the south-central Athabasca Basin (Canada) and straddles the unconformity between early Paleoproterozoic to Archean metasedimentary and metavolcanic rocks and granitoids, and the clastic sediments of the Paleoproterozoic Athabasca Group. Although it has most characteristics of an unconformity-related uranium deposit, the Centennial deposit is atypical in that it is not directly associated with an electromagnetic conductor (there is a paucity of graphite in the basement) or with a major reverse fault zone; it is distal from a major fluid conduit (ca. 300 to 400 m from the Dufferin Lake Fault), has low Ni, Cu, Co, Zn, and Pb contents, and contains an unusually large amount (up to 5%) of secondary uranyl minerals. Additionally, a network of diabase dikes and sills is observed at Centennial, seemingly intruding the main U mineralization of massive uraninite, based on the relatively sharp contacts between the diabase dike and the high-grade U mineralization. The pre-U alteration assemblage at Centennial includes kaolinite, illite, and sudoite, which have been formed by fluids with isotopic and chemical compositions that are comparable with those from other sandstone-hosted unconformity-type U deposits in the Athabasca Basin. Pre-U illite-related fluids have δ 18 O of ca. 3‰ and δD of ca.-40‰, whereas pre-U chlorite-related fluids have δ 18 O between 1.7 and 4.3‰ and δD between-18 and 1‰. Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) U/Pb dating of the various U phases indicates that initial mineralization, represented by disseminated uraninite found directly to the north-northeast of the Centennial deposit, occurred at ca. 1.6 Ga. The main U mineralization, represented by massive and strongly altered uraninite, followed at an unknown time. A minor (<5%) unaltered uraninite formed from the local remobilization of the main massive uraninite at ca. 380 Ma. The main uranyl mineral, uranophane, formed last, at ca. 2 Ma. The recurrence of local U remobilization might have been facilitated by the persisting high permeability of the sandstones in the area due to the nearby Dufferin Lake Fault and to the emplacement of the diabase dikes. The usefulness of Pb isotopes for exploration is demonstrated at the Centennial deposit, with strongly radiogenic Pb isotope signatures close to the deposit and a common Pb signature observed at a distance of a few km from the deposit.

Economic Geology, 2009

ABSTRACT The Spring Point barren alteration system and the Maurice Bay subeconomic uranium deposi... more ABSTRACT The Spring Point barren alteration system and the Maurice Bay subeconomic uranium deposit, situated oil the northwest rim of the Athabasca Basin, northern Saskatchewan,an, are hosted by the sandstones and conglomerates of the Fair Point Formation of them Athabasca Group. Macroscopic observations indicate two different styles of alteration for the two systems: chlorite-dominated, partly reduced alteration at Spring Point, and illite-dominated, strongly oxidized alteration at Maurice Bay. The paragenetic sequence's developed for each area are similar, but the crystal chemistry of the alteration minerals differs markedly, indicating that the alteration fluids at Spring Point were richer ill Mg and Ca than at Maurice Bay; this is consistent with a predominantly basement origin for the former. Stable isotope analyses of clay alteration minerals indicate that, in particular, the chlorite-related fluids from Spring Point have a basement signature delta O-18 = 3.5 parts per thousand and delta D = -13 parts per thousand), whereas chlorite front Maurice Bay is more consistent with a mixture of basement and basinal fluids (delta O-18 = 5.2 parts per thousand and delta D = -28 parts per thousand). The absence of uranium-transporting basinal fluids at the critical time when reducing basement fluids were producing chlorite alteration is likely the single most important cause for the lack of uranium mineralization at Spring Point.

Economic Geology, 2014

The Centennial unconformity-related uranium deposit represents the first significant uranium mine... more The Centennial unconformity-related uranium deposit represents the first significant uranium mineralization along the Snowbird tectonic zone in the south-central part of the Athabasca Basin. The deposit is associated with a steeply WNW-dipping contact between the Virgin Schist Group and mylonitic granite of uncertain age. Virgin Schist Group rocks in the deposit area include phyllites, impure quartzite, and quartzite. Medium- to coarse-grained microcline “augen” porphyroclasts characterize the granite. The quartzite, being resistant to weathering, forms a paleotopographic high flanked by a paleotalus which formed prior to Athabasca Group sedimentation. Diabase, petrographically and geochemically similar to the 1.27 Ga Mackenzie dikes, intrudes the mineralized trend along brittle structures in the basement rocks and Athabasca Group. A detailed paragenetic study of the deposit area reveals a protracted history that is related to the episodic reactivation of brittle structures and associated fluid movement along this significant structural corridor. Retrograde metamorphism converted biotite to chamosite at temperatures between 335° to 350°C. Weathering caused the breakdown of microcline and the dissolution of quartz prior to erosion and deposition of the Athabasca Group, which started at about 1750 Ma. Compaction and diagenesis resulted in quartz overgrowths and development of a diagenetic clay assemblage of illite and sudoite at temperatures between 150° and 200°C, which was broadly synchronous with primary mineralization. Clinochlore, euhedral quartz, carbonate, and pyrite was developed after the intrusion of the diabase under reducing conditions, primarily at temperatures between 270° to 320°C. Uranium remobilization and alteration of uraninite to coffinite appears to have taken place after the emplacement of the diabase dikes. Kaolinite and uranophane form last in the paragenetic sequence and probably form at relatively low temperatures.

The Canadian Mineralogist, 2016

Mineralium Deposita, 2016

Mineralium Deposita, 2015

Economic Geology, 2012

Economic Geology, 2009

Economic Geology, 2014