Water quality condition and trend in North Queensland waterways

The Queensland Environmental Protection Agency monitored water quality at 133 sites in North Queensland waterways between Cooktown and Bundaburg from 1992 to 2001. Condition of the waterways was rated by comparing recent data with the Queensland Water Quality Guidelines. Long-term trends were analysed using a censored regression technique that incorporates the effects of flow, temperature, seasonality and allows for long-term non-linear trends. Many sites were in good condition; those in poor condition were usually impacted by point source discharges; those in moderate condition were usually impacted by agricultural land use. There were no consistent long-term trends across the whole region. Recommendations for future programs include incorporating pressure indicators, ensuring high standards of quality assurance, including covariates such as rainfall in trend assessment and continuing programs over more than 10 years to allow detection of trends due to changes in land-use.     

Effects of water use on arsenic release to well water in a confined aquifer

Field-based experiments were designed to investigate the release of naturally occurring, low to moderate (< 50 microg/L) arsenic concentrations to well water in a confined sandstone aquifer in northeastern Wisconsin. Geologic, geochemical, and hydrogeologic data collected from a 115 m2 site demonstrate that arsenic concentrations in ground water are heterogeneous at the scale of the field site, and that the distribution of arsenic in ground water correlates to solid-phase arsenic in aquifer materials. Arsenic concentrations in a test well varied from 1.8 to 22 microg/L during experiments conducted under no, low, and high pumping rates. The quality of ground water consumed from wells under typical domestic water use patterns differs from that of ground water in the aquifer because of reactions that occur within the well. Redox conditions in the well can change rapidly in response to ground water withdrawals. The well borehole is an environment conducive to microbiological growth, and biogeochemical reactions also affect borehole chemistry. While oxidation of sulfide minerals appears to release arsenic to ground water in zones within the aquifer, reduction of arsenic-bearing iron (hydr)oxides is a likely mechanism of arsenic release to water having a long residence time in the well borehole.     

Quantity, composition, and source of sediment collected in sediment traps along the fringing coral reef off Molokai, Hawaii

Sediment traps were used to evaluate the frequency, cause, and relative intensity of sediment mobility/resuspension along the fringing coral reef off southern Molokai (February 2000-May 2002). Two storms with high rainfall, floods, and exceptionally high waves resulted in sediment collection rates>1000 times higher than during non-storm periods, primarily because of sediment resuspension by waves. Based on quantity and composition of trapped sediment, floods recharged the reef flat with land-derived sediment, but had a low potential for burying coral on the fore reef when accompanied by high waves. The trapped sediments have low concentrations of anthropogenic metals. The magnetic properties of trapped sediment may provide information about the sources of land-derived sediment reaching the fore reef. The high trapping rate and low sediment cover indicate that coral surfaces on the fore reef are exposed to transient resuspended sediment, and that the traps do not measure net sediment accumulation on the reef surface.     

鄂东丰山矿田卡林型金矿地质地球化学特征

鄂东丰山矿田主要由丰山 (封山洞 )铜矿床、鸡笼山金铜矿床和李家湾铜矿床组成。经野外调查和室内研究 ,确认矿田内存在卡林型金矿 ,金平均品位约 5× 1 0 -6,远景储量在大型以上。该卡林型金矿的主要特征是 :(1 )分布于丰山斑岩体周围的中酸性岩脉发育区 ;(2 )容矿岩石为下三叠统大冶组薄层状 -纹层状和角砾状碳酸盐岩 ;(3)矿体主要受高角度断层控制 ,通常产于岩脉的一侧或附近 ;(4 )矿石普遍具白色细网脉状方解石化和碳泥化 ,裂面上常见黑色碳质被膜 ;(5 )金主要为次显微金 ;(6 )成矿物质主要来自矿源层 ,部分来自岩浆 ,成矿热液水主要来自大气降水     

大兴安岭北部雄关地区倭勒根岩群大网子岩组火山岩地球化学特征

雄关地区的倭勒根岩群大网子岩组主要为变碎屑岩夹变流纹岩和变粗面安山岩.利用ICP-MS仪器对变粗面安山岩进行锆石U-Pb年龄测定,结果显示变粗面安山岩锆石²⁰⁶Pb/²³⁸U年龄为443.8~783.8 Ma,获得ICP-MS锆石U-Pb同位素谐和年龄为463.7±2.1 Ma,加权平均年龄为463.6±6.4 Ma（ⁿ=10,MSWD=0.073）.所测锆石振荡环带较发育,Th/U值一般为0.42~1.76,具有岩浆成因特征.该年龄代表粗面安山岩形成年龄,认为其形成于中奥陶世,与区域大网子岩组形成时代（寒武纪-早志留世）一致.大网子岩组粗面安山岩属碱钙系列准铝质岩石,铕异常不显著,相对亏损高场强元素,富集大离子亲石元素.岩石具有壳幔混源特征,形成于陆缘环境,与古亚洲洋壳俯冲有关.