Brooklyn College of CUNY
Earth and Environmental Science
Tin is a rare metal that is essential for making bronze, the defining technology of the Bronze Age. The source(s) of tin for Aegean bronze is undetermined but several small Bronze Age tin mines have been documented in the circum-Aegean... more
Tin is a rare metal that is essential for making bronze, the defining technology of the Bronze Age. The source(s) of tin for Aegean bronze is undetermined but several small Bronze Age tin mines have been documented in the circum-Aegean region. The discovery of Bronze Age archaeological sites in West Serbia near a tin placer deposit on the flanks of Mt. Cer led to an investigation of this site as a potential additional Bronze Age tin mine in the region. Geochemical prospecting of stream sediments flowing from Mt. Cer allowed for categorization of streams based on relative tin grade. Tin grade is highest in the Milinska River, a likely combination of a broad catchment area with multiple ore-bearing tributaries, and a topographic profile that favors the accumulation of placer deposits. A survey of cornfields along the southern pluton margin discovered archaeological sites spanning the Neolithic to the Iron Age. Unlike older and younger sites, those of the Bronze Age were found only along the Milinska and Cernica Rivers where placer tin grades are highest, but appear to be absent where tin is scarce or absent. This suggests that these sites were associated with the exploitation of the tin ore. C
- by Andrea H Mason and +4
- •
Tin is a rare metal that is essential for making bronze, the defining technology of the Bronze Age. The source(s) of tin for Aegean bronze is undetermined but several small Bronze Age tin mines have been documented in the circum-Aegean... more
Tin is a rare metal that is essential for making bronze, the defining technology of the Bronze Age. The source(s) of tin for Aegean bronze is undetermined but several small Bronze Age tin mines have been documented in the circum-Aegean region. The discovery of Bronze Age archaeological sites in West Serbia near a tin placer deposit on the flanks of Mt. Cer led to an investigation of this site as a potential additional Bronze Age tin mine in the region. Geochemical prospecting of stream sediments flowing from Mt. Cer allowed for categorization of streams based on relative tin grade. Tin grade is highest in the Milinska River, a likely combination of a broad catchment area with multiple ore-bearing tributaries, and a topographic profile that favors the accumulation of placer deposits. A survey of cornfields along the southern pluton margin discovered archaeological sites spanning the Neolithic to the Iron Age. Unlike older and younger sites, those of the Bronze Age were found only along the Milinska and Cernica Rivers where placer tin grades are highest, but appear to be absent where tin is scarce or absent. This suggests that these sites were associated with the exploitation of the tin ore. C
Isotopic analysis has proved to be an effective approach to determine the provenance of copper ore sources for the production of bronze artifacts. More recently, methods for Sn isotopic analysis of bronze have been developed. However, the... more
Isotopic analysis has proved to be an effective approach to determine the provenance of copper ore sources for the production of bronze artifacts. More recently, methods for Sn isotopic analysis of bronze have been developed. However, the viability of tin isotopes as a means to define groupings that may be attributed to varying ore sources, production methods, or recycling is still in question. In part, this is due to the numerically and/or geographically limited nature of published datasets. This study reports on the Sn isotopic composition of 52 artifacts from the later Bronze Age (1500-1100 BCE) from Serbia and western Romania. The majority of samples cluster between 0.4 and 0.8 per mil for d 124 Sn, and 0.2 and 0.4 per mil for d 120 Sn (relative to NIST SRM 3161A), and this isotopic grouping of bronze artifacts occurs across Serbia. However, groupings of isotopically heavier and lighter artifacts are evident, and each corresponds to a more limited geographic range. Artifacts associated with higher dSn values are limited to the Vojvodina region of northern Serbia, whereas a cluster of bronzes with lower Sn-isotopic signatures are constrained to the Banat along the Serbia-Romania border, and Transylvania. One low-value outlier corresponds to an uncontextualized find near Kru sevac at the southern extent of the study area. Geographic correlation of the low-value cluster with known tin mineralization in Transylvania, and the moderate-value cluster with placer tin deposits of western Serbia, suggests that these distinct bronze Sn-isotopic signatures might reflect exploitation of different tin ores. The small cluster of high Sn-isotopic values from bronzes from the Vojvodina region might reflect bronze recycling in this area that lies furthest from both known tin ore sources.
Increased interest in the fractionation of Sn isotopes has led to the development of several techniques for preparing cassiterite (SnO 2 , the primary ore of Sn) for isotopic analysis. Two distinct methods have been applied in recent... more
Increased interest in the fractionation of Sn isotopes has led to the development of several techniques for preparing cassiterite (SnO 2 , the primary ore of Sn) for isotopic analysis. Two distinct methods have been applied in recent isotopic studies of cassiterite: (a) reduction to tin metal with potassium cyanide (KCN) at high temperature (800 °C), with subsequent dissolution in HCl, and (b) reduction to a Sn solution with hydriodic acid (HI) at low temperature (100 °C). This study compares the effectiveness and accuracy of these two methods and contributes additional methodological details. The KCN method consistently yielded more Sn (> 70% in comparison with < 5%), does not appear to fractionate Sn isotopes at high temperatures over a 2-hour period and produced consistent Sn isotope values at flux mass ratios of ≥ 4:1 (flux to mineral) with a minimum reduction time of 40 min. By means of a distillation experiment, it was demonstrated that HI could volatilise Sn, explaining the consistently low yields by this method. Furthermore, the distillation generated Sn vapour, which is up to 0.38‰ per mass unit different from the starting material, the largest induced Sn fractionation reported to date. Accordingly, the HI method is not recommended for cassiterite preparation for Sn isotopic analysis.
- by Wayne Powell and +1
- •
- Stable Isotope Analysis, Archaeometry
a b s t r a c t a r t i c l e i n f o Keywords: Cambrian Burgess Shale Seeps Mud mounds Cathedral Escarpment Sequence stratigraphy
Tin is a rare metal that is essential for making bronze, the defining technology of the Bronze Age. The source(s) of tin for Aegean bronze is undetermined but several small Bronze Age tin mines have been documented in the circum-Aegean... more
Tin is a rare metal that is essential for making bronze, the defining technology of the Bronze Age. The source(s) of tin for Aegean bronze is undetermined but several small Bronze Age tin mines have been documented in the circum-Aegean region. The discovery of Bronze Age archaeological sites in West Serbia near a tin placer deposit on the flanks of Mt. Cer led to an investigation of this site as a potential additional Bronze Age tin mine in the region. Geochemical prospecting of stream sediments flowing from Mt. Cer allowed for categorization of streams based on relative tin grade. Tin grade is highest in the Milinska River, a likely combination of a broad catchment area with multiple ore-bearing tributaries, and a topographic profile that favors the accumulation of placer deposits. A survey of cornfields along the southern pluton margin discovered archaeological sites spanning the Neolithic to the Iron Age. Unlike older and younger sites, those of the Bronze Age were found only along the Milinska and Cernica Rivers where placer tin grades are highest, but appear to be absent where tin is scarce or absent. This suggests that these sites were associated with the exploitation of the tin ore. C
Study of noncalcareous algal fossils is problematic due to their broadly defined taxonomy and lack of preserved features by which modern algae are classified. Four distinct morphologically simple, enigmatic fossils from the Wheeler... more
Study of noncalcareous algal fossils is problematic due to their broadly
defined taxonomy and lack of preserved features by which modern algae are
classified. Four distinct morphologically simple, enigmatic fossils from the
Wheeler Formation were analyzed using Raman spectroscopy, and
elemental mapping by electron microbeam techniques. These fossils have
been interpreted as dissociated algal fragments, and accordingly, were
compared to known algal fossils: Yuknessia simplex (green alga; Spence
Shale), Marpolia spissa (cyanobacteria; Burgess Shale), and Margaretia
dorus (green alga; Burgess and Wheeler formations). All fossils examined
were composed of carbonaceous films, at least in part, but varied with
respect to secondary mineral coatings: iron oxides were associated with the
surfaces of all three algal species to some degree, and in addition,
Margaretia dorus exhibited silicification. Fossils characterized by a thin,
wispy, filamentous form (Linear Morphotype 2) display mineralogical and
morphological similarities with Marpolia spissa, but lack the characteristic
longitudinal striping of this species. Filamentous fossils with a coiled form
were the only fossils found to contain chlorite. These fossils are interpreted
to be fecal strings. Stubby, linear fossils (Linear Morphotype 1) that
commonly have been interpreted as fragmented Yuknessia simplex exhibit
neither the mineralogical nor the microtextural features of this algal fossil,
making this interpretation unlikely. As with Linear Morphotype 1, fossils
of Morania fragmenta lack secondary iron oxides and phyllosilicates.
Accordingly, they are interpreted to have been composed of labile material
that preserves only under inhospitable conditions such as sustained anoxia.
defined taxonomy and lack of preserved features by which modern algae are
classified. Four distinct morphologically simple, enigmatic fossils from the
Wheeler Formation were analyzed using Raman spectroscopy, and
elemental mapping by electron microbeam techniques. These fossils have
been interpreted as dissociated algal fragments, and accordingly, were
compared to known algal fossils: Yuknessia simplex (green alga; Spence
Shale), Marpolia spissa (cyanobacteria; Burgess Shale), and Margaretia
dorus (green alga; Burgess and Wheeler formations). All fossils examined
were composed of carbonaceous films, at least in part, but varied with
respect to secondary mineral coatings: iron oxides were associated with the
surfaces of all three algal species to some degree, and in addition,
Margaretia dorus exhibited silicification. Fossils characterized by a thin,
wispy, filamentous form (Linear Morphotype 2) display mineralogical and
morphological similarities with Marpolia spissa, but lack the characteristic
longitudinal striping of this species. Filamentous fossils with a coiled form
were the only fossils found to contain chlorite. These fossils are interpreted
to be fecal strings. Stubby, linear fossils (Linear Morphotype 1) that
commonly have been interpreted as fragmented Yuknessia simplex exhibit
neither the mineralogical nor the microtextural features of this algal fossil,
making this interpretation unlikely. As with Linear Morphotype 1, fossils
of Morania fragmenta lack secondary iron oxides and phyllosilicates.
Accordingly, they are interpreted to have been composed of labile material
that preserves only under inhospitable conditions such as sustained anoxia.
- by Kimberly Handle and +2
- •
- Burgess Shale
Many aspects of the timing and genesis of the Archean Hemlo gold deposit are unresolved; pre-, syn-and postmetamorphic models have been proposed. The presence of abundant low-temperature sulfide minerals udthin highly deformed,... more
Many aspects of the timing and genesis of the Archean Hemlo gold deposit are unresolved; pre-, syn-and postmetamorphic models have been proposed. The presence of abundant low-temperature sulfide minerals udthin highly deformed, sillimanite-grade host rocks has been used to support a postmetamorphic origin for the deposit. However, the present Sb-As-Hg ore assemblage, including cinnabar-realgar-orpiment assemblages, developed through a sequence of exsolution events during postpeak metamorphic cooling. At peak metamorphisre, most of the As and Hg, along with T1, Cu, Zn, and minor Fe, was incorporated into a high-temperature antimonian sulfosalt. In the lower amphibolite facies or upper greenschist facies, impure (Hg, Zn)S exsolved fi'om the high-temperature phase. An impure chaleopyrite and native antimony exsolved from the host sulfosalt soon after, leaving behind an Sb2S•-As2S3 solid solution. Further cooling resulted in the exsolution of cinnabar and mercurian sphalerite from the (Hg,Zn)S. Impurities in the cinnabar and ehalcopyrite exsolved to form aktashite, arsenopyrite and native antimony. Eventually, orpiment exsolved from the arsenic-bearing stibnite. Late, retrograde events converted the free orpiment to realgar and remobilized the realgar over short distances, along with cinnabar and native antimony. The history of sequential sulfide exsolution, along with the deformed nature of the Sb-As-Hg-bearing veins, and their metamorphosed alteration selvages, suggests that the metals were introduced prior to, or during, peak metamorphism. Introduction WITH its estimated 20 million ounces (Moz) of gold, the Henrio gold deposit of northwestern Ontario is the largest gold deposit currently being mined in Canada. In addition to its economic importance, Hemlo is of interest because of its atypical alteration style and metal associations, including Mo, As, Hg, and Sb. The highly deformed nature of the deposit and the high metamorphic grade of the host rocks has obscured many relationships at the mine site and has resulted in a broad spectrum of genetic models being proposed for the origin of the deposit. Currently discussed ideas for the genesis of Hemlo include premetamorphie porphyry mineralization (Kuhns et al., 1994; Johnston, 1996), syn-to postmetamorphic shear zone-related mineralization (Hugon, 1986; Corfu and Muir, 1989), and postmetamorphic multistage replacement mineralization (Pan and Fleet, 1995).
Textural relations between Al 2 SiO 5 phases, and deformation fabrics, provide constraints on the metamorphic history of the Hemlo gold deposit. Kyanite in the deposit is most common within and on the margins of boudinaged quartz ±... more
Textural relations between Al 2 SiO 5 phases, and deformation fabrics, provide constraints on the metamorphic history of the Hemlo gold deposit. Kyanite in the deposit is most common within and on the margins of boudinaged quartz ± realgar veins, and less commonly as rotated porphyroblasts within the matrix of schistose rocks. Kyanite predates the main (D2) schistosity. Sillimanite postdates kyanite, occurring irregularly as discrete knots and foliae that run parallel to, but sometimes cut across, the principal (D2) foliation, indicating that sillimanite postdates the D2 foliation. We regard kyanite to be part of the peak metamorphic assemblage, with sillimanite representing a partial later overprint most likely related to fluid infiltration. Rare andalusite occurs in two associations: as late-stage, clean, idioblastic crystals; and as large, fractured grains, locally overprinted by sillimanite, in boudinaged quartz-realgar veins. We suggest two possible origins for this second form of andalusite, one involving generally late growth, the second involving early growth prior to the development of peak metamorphic kyanite. Although not unambiguous, we prefer the second scenario. P-T conditions from petrogenetic grid constraints, and new geothermobarometric estimates, indicate 6-7 GPa, 600-650°C for the peak kyanite grade metamorphism (ca. 2677 Ma?), and 4-5 GPa, 600°C for the later sillimanite overprint (ca. 2672 Ma?). We see these two events as part of an evolving P-T path in a single metamorphic event. In our early andalusite scenario, the andalusite may have formed from pyrophyllite breakdown at 2-4 GPa, 450°C, possibly associated with emplacement of the regional suite of granodiorite plutons (ca. 2686 Ma). Late andalusite formed sporadically on the retrograde path. The occurrence of deformed andalusite and aligned kyanite in and on the margins of boudinaged auriferous realgar-stibnite-quartz veins provides evidence in support of a premetamorphic mineralization event.
Four science programs at our public urban liberal arts college have struggled to attract and retain majors: physics, environmental studies, geology, and teaching science. The Brooklyn Opportunities in Science and Careers (BOSC) program... more
Four science programs at our public urban liberal arts college have struggled to attract and retain majors: physics, environmental studies, geology, and teaching science. The Brooklyn Opportunities in Science and Careers (BOSC) program aims to increase student participation in these majors using a new career-focused strategy to recruit students. Our hypothesis is that by providing capable students with information about employment prospects in diverse sciencerelated careers during the summer before their freshman year, we could increase the total number of majors and graduates in these science departments. Field trips to explore science careers in unanticipated settings and a Career Investigation Project are the core innovations of the BOSC program. Students work in collaborative groups to investigate potential careers, gaining skills important in almost all careers such as teamwork and preparing and delivering presentations. Institutional and program evaluation data indicate that the BOSC program has had a significant positive impact on both the program participants and on the cultures and enrollments in the target departments.
Deciphering the oxygenation potential of bottom waters during deposition of the fossiliferous strata of the Burgess Shale is key to understanding the paleoecology of the organisms preserved as fossils and the processes involved in their... more
Deciphering the oxygenation potential of bottom waters during deposition of the fossiliferous strata of the Burgess Shale is key to understanding the paleoecology of the organisms preserved as fossils and the processes involved in their preservation. Methods of paleo-redox determination that are based upon trace fossils, organic carbon content, or size analysis of pyrite framboids are problematic when applied to the Burgess Shale. Fortunately, patterns in redox-sensitive trace elements hold great potential for determining paleo-redox conditions for these greenschist-facies rocks because they are independent of both age and metamorphic grade. Four Burgess Shale-Type (BST) fossil-bearing sections were studied; three lie within the Burgess Shale Formation, whereas one lies within the slightly younger Duchesnay unit of the Middle Chancellor Formation. The geochemical proxies of seawater redox conditions that were used are Mo, U/Th, V/Cr, V/(V+Ni), Ni/Co and V/Sc. Each of these redox-sensitive indices suggests that oxygenated conditions prevailed in the overlying seawater during deposition of beds within which BST preservation developed. Non-fossiliferous beds at the base of the Mt. Stephen Trilobite Beds yield three geochemical indices (V/[V+Ni], V/Sc, Ni/Co) that indicate deposition under dysoxic to anoxic conditions. Thus the only beds to have been deposited under anoxic conditions are barren of fossils of soft-bodied taxa, further contradicting the notion that bottom-water anoxia is a factor in BST preservation. The laminated nature of the Burgess Shale and evidence for subsurface anoxia, coupled with evidence for oxygenated bottom waters, presence of bacterial mats, and surficial trace fossils suggest that the Burgess Shale was deposited in the exaerobic zone (oxic^anoxic boundary at the waterŝ ediment interface). Implications of this reinterpretation of the depositional environment of the Burgess Shale include:
- by Christopher J Collom and +1
- •
- Burgess Shale
Metamorphosed silty mudstones of the Burgess Shale and Stephen Shale formations record a polymetamorphic history. An early greenschist-facies event associated with burial by Paleozoic strata produced a nearly ubiquitous bedding-parallel... more
Metamorphosed silty mudstones of the Burgess Shale and Stephen Shale formations record a polymetamorphic history. An early greenschist-facies event associated with burial by Paleozoic strata produced a nearly ubiquitous bedding-parallel cleavage (S 1 ). Tectonic exhumation during the formation of the southern Canadian Rocky Mountains produced a domainal subgreenschist-facies retrograde overprint in which a high-angle crenulation cleavage (S 2 ) was developed. Whereas all rocks have experienced these two events, the degree of deformation and fossil preservation varies with position relative to the Cathedral Escarpment. This paleosubmarine cliff resulted in a zone of reduced deformation within adjacent strata by buttressing them during burial and deflecting deformation during orogenesis. Fossil-bearing strata are composed of a typical greenschist assemblage of muscovite-chlorite-quartz-albite, are devoid of clays, and contain an average of 0.28% organic carbon. This typical metamudstone assemblage is consistent with the typical whole-rock composition of these rocks which tends to be richer in K and Al and poorer in Fe relative to the Post-Archean Average Shale. These mineralogical-compositional characteristics suggest that the premetamorphic clay assemblage was likely illite-smectite-kaolinite, with no evidence of highly reactive species such as nontronite or Na-montmorillonite. This is contrary to the required conditions for taphonomic models involving organic preservation due to clay-related suppression of decomposition-related reactions. Metamorphism of the Burgess Shale has also reduced the total organic carbon content to <20% of initial values. This must be considered in any models that involve interpretation of organic carbon in diagenetic processes (e.g., fossil formation and determination of paleoredox conditions).
TRUST, or Teacher Renewal for Urban Science Teaching, is a National Science Foundation funded Earth science teacher preparation partnership between the American Museum of Natural History and Brooklyn and Lehman Colleges of the City... more
TRUST, or Teacher Renewal for Urban Science Teaching, is a National Science Foundation funded Earth science teacher preparation partnership between the American Museum of Natural History and Brooklyn and Lehman Colleges of the City University of ...
Abstract: In the context of two summer courses (a science methods course and a geology course), the authors worked with 40 elementary and high school teachers enrolled in Brooklyn College's MSE programs in elementary education or... more
Abstract: In the context of two summer courses (a science methods course and a geology course), the authors worked with 40 elementary and high school teachers enrolled in Brooklyn College's MSE programs in elementary education or secondary science ...
- by Maritza Macdonald and +2
- •
- Science Education, Higher Education
Mineral equilibria in the system Ca0-Mg0-A120,-Si02-H20 provide a basis for mapping of four reaction isograds and one bathograd in the low-pressure transition from subgreenschist to greenschist facies. Most of the Matachewan area of the... more
Mineral equilibria in the system Ca0-Mg0-A120,-Si02-H20 provide a basis for mapping of four reaction isograds and one bathograd in the low-pressure transition from subgreenschist to greenschist facies. Most of the Matachewan area of the Abitibi greenstone belt is in the lower-pressure bathomne, as indicated by the widespread occurrences of the subassemblage Prh-Chl. The higher-pressure bathozone is indicated by two Occurrences of Pmp-Act-Ep-Qtz, but in these samples the bathograd is displaced to anomalously low pressure by the high Fe content of the coexisting minerals. This illustrates the need to analyse coexisting minerals, calculate activities of end-member species, and compute P-T curves for individual samples before interpreting the isograd/bathograd pattern.
- by Dugald Carmichael and +1
- •
- Geology, Metamorphic Geology