Baguio Mineral District: An oceanic arc witness to the geological evolution of northern Luzon,Philippines

The Baguio Mineral District exposes rock formations that evince the geological and tectonic evolution of this district from a subduction‐related marginal basin to an island arc setting. Available onshore and offshore data are consistent with an Early (onset phase) to Middle (developed phase) Miocene arc polarity reversal from the east (termination of subduction along the proto‐East Luzon Trough) to the west (initiation of subduction along the Manila Trench). Geophysical modeling and geochemical data calculation showed a 30 ± 5 km crustal thickness for the mineral district. Subduction‐related multiple arc magmatism and ophiolite accretion contributed to crustal thickening. Recent information on the Oligo–Miocene Zigzag and Klondyke formations in the mineral district reveal that the marginal basin, where these rocks were deposited, has received eroded materials from adjacent terrains characterized by siliceous lithologies. Furthermore, adakitic rocks, high permeable zones and extensional zones which are exploration markers applied to identify possible mineralization targets, are prevalent in the mineral district. The geological evolution that the district had undergone mimics the evolution of island arcs worldwide in general and northern Luzon in particular.     

洛阳铲钻探在菲律宾迪纳加特岛汇洋镍矿区快速评价中的应用

在菲律宾迪纳加特岛汇洋镍矿区第二期勘查中,采用以洛阳铲钻探为主、浅井为辅的勘探方式,取得了较好的勘查效果。洛阳铲钻探和浅井勘探的镍品位曲线具有相似的特征,可以互相印证;铁品位曲线具有相同的变化趋势。与浅钻勘探资料对比,洛阳铲的镍品位变化趋势与浅钻的结果非常相似。因此认为,用洛阳铲勘探品位变化小的风化壳型矿床的浅部是适宜的,如果将其与浅井、浅钻结合使用,将在风险勘查中独具优势。     

Mineral Paragenesis of the Lepanto Copper and Gold and the Victoria Gold Deposits, Mankayan Mineral District, Philippines

Abstract: Mineral paragenesis of the alteration, ore and gangue minerals of the Lepanto epithermal copper‐gold deposit and the Victoria gold deposit, Mankayan Mineral District, Northern Luzon, Philippines, is discussed. The principal ore minerals of the Lepanto copper‐gold deposit are enargite and luzonite, with significant presence of tennantite‐tetrahedrite, chalcopyrite, sphalerite, galena, native gold/electrum and gold‐silver tellurides. Pervasive alteration zonations are commonly observed from silicification outward to advanced argillic then to propylitic zone. The ore mineralogy of the Lepanto copper‐gold deposit suggests high f_S2 in the early stages of mineralization corresponding to the deposition of the enargite‐luzonite‐pyrite assemblage. Subsequent decrease in the f_S2 formed the chalcopyrite‐tennantite‐pyrite assemblage. An increase in the f_S2 of the fluids with the formation of the covellite‐digenite‐telluride assemblage caused the deposition of native gold/electrum and gold‐silver tellurides. The principal ore minerals of the Victoria gold deposit are sphalerite, galena, chalcopyrite, tetrahedrite and native gold/electrum. The alteration halos are relatively narrow and in an outward sequence from the ore, silica alteration grades to illitic‐argillic alteration, which in turn grades to propylitic alteration. The Victoria gold mineralization has undergone early stages of silica supersaturation leading to quartz deposition. Vigorous boiling increased the pH of the fluids that led to the deposition of sulfides and carbonates. The consequent decrease in H₂S precipitated the gold. Gypsum and anhydrite mainly occur as overprints that cut the carbonate‐silica stages. The crosscutting and overprinting relationships of the Victoria quartz‐gold‐base metal veins on the Lepanto copper‐gold veins manifest the late introduction of near neutral pH hydrothermal fluids.     

Analysis and mapping of geochemical anomalies using logratio-transformed stream sediment data with censored values

There is lack of research and documentation of actual (as opposed to theoretical) benefits (e.g., mineral deposit discovery) of developments in compositional data analysis and imputation of censored values to mineral exploration geochemistry. In the present study, analyses of logratio- and ln-transformed stream sediment geochemical data containing ca. 30% of samples with censored values of a pathfinder element for the mineral deposit-type of interest yielded the following findings. Exclusion of those samples supports interpretation of multi-element anomalies reflecting the presence of mineralization. However, the multi-element anomaly maps obtained by exclusion of those samples are barely better than the multi-element anomaly maps derived by inclusion of those samples after replacing the censored values with 1/2 of detection limit or with imputed values. Logratio (i.e., alr, clr, or ilr) transformation, compared to ln-transformation, of stream sediment geochemical data does not improve mapping of pathfinder element anomalies reflecting the presence of mineralization. However, stream sediment geochemical data, excluding or including censored values (replaced with 1/2 of detection limit or with imputed values), should be clr- or ilr-transformed to enhance recognition of anomalous multi-element associations reflecting the presence of mineralization. The anomaly maps of multi-element associations derived from ilr-transformed data are better, albeit slightly, than the anomaly maps of multi-element associations derived from clr-transformed data. In the present study, the main benefit of either clr- or ilr-transformation, compared to either ln- or alr-transformation, of stream sediment geochemical data is the enhancement of anomalous multi-element associations reflecting the presence of mineralization. This is an important benefit because variations in trace element concentrations in regional-scale stream sediment geochemical data are mostly due to lithology and other factors (or processes) unrelated to mineralization. Further investigations of various exploration geochemical data are needed to demonstrate and document the actual (as opposed to theoretical) benefits of developments in compositional data analysis and imputation of censored values to mineral exploration.     

Regulating migration to Australia and back to the Philippines: Applying a ‘diaspora strategies’ framework

This paper examines circular labour migration between Australia and the Philippines by bringing Australian immigration policies and Philippine diaspora strategies under the same analytical framework. An extensive Philippine bureaucracy regulates migrants at each stage of the circular migration cycle, and as a sending state it has an interest in migrants staying temporarily in host countries such as Australia. The requirement to return home at the end of an overseas work contract compels migrants to remain attached to the sending state, their homeland, and return subsequently. However, Australia is allowing a route for temporary migrants to apply for permanent residency while in the host country. This has implications for sending states that rely on migrant ties to the homeland. The paper argues that analysing the intersections between the themes of migration, development and diaspora strategies reveals the multiple meanings of temporariness during migration and in migration studies. It questions whether associating temporariness with precariousness and marginalization is an accurate representation of the complex conditions underpinning circular labour migration.     

Nutrient loadings and deforestation decrease benthic macroinvertebrate diversity in an urbanised tropical stream system

Lotic ecosystems in urban areas are severely impacted by anthropogenic environmental stressors, such as deforestation and nutrient pollution, due to socioeconomic activities in the catchment. To work out measures for identification and mitigation of concurrent multiple stressors to a stream system, it is necessary to assess the relative importance of impacts by the individual stressors. Here we aimed to discriminate the covarying effects of nutrient pollution and deforestation on benthic macroinvertebrate communities in an urbanised tropical stream system. In the Silang-Santa Rosa Subwatershed (SSRS) of Laguna de Bay, benthic macroinvertebrates and physicochemical environments were investigated at 13 sites varying in human population density, riparian canopy, and land-use pattern as indicated by geographic information systems in the catchment. Regression and multivariate analyses were performed to identify the drivers of the biodiversity loss and understand its underlying mechanisms. In the SSRS, where rapid economic growth took place without updating poorly installed wastewater treatment plants (WWTPs), domestic activity indicated by human population density in the catchment was the primary factor in generating heavy phosphorous loadings (mean total phosphorus = 0.91; range = 0–1.50 mg/l) that caused hypoxia (mean dissolved oxygen = 2.98; range = 0.13–6.27 mg/l) in stream waters and subsequently reduced macroinvertebrate diversity (mean H’ = 0.91; SD ± 0.61). Nutrient and organic pollution and riparian deforestation explained 53.5% and 9.7% of the variation of benthic macroinvertebrate communities in SSRS, respectively. Given such scenario, additional WWTPs servicing urban developments and improved riparian canopy cover in the SSRS can be both strategic and cost-effective in the initial steps of environmental mitigation in urbanised streams, especially in rapidly developing countries.     

Impact of milk fish farming in the tropics on potentially pathogenic vibrios

Ratios of sucrose-negative to sucrose-positive vibrios on TCBS agar (suc−/suc+) indicate the abundance of potential human pathogenic non-cholera vibrios in coastal mariculture environments of the Lingayen Gulf (Philippines. In guts of adult maricultured milkfish (Chanos chanos) of suc− vibrios reached extreme peak values ranging between 2 and 545 million per g wet weight. Suc− vibrios outnumbered suc+ vibrios in anoxic sediments, too, and were rarely predominant in coastal waters or in oxidized sediments. Suc−/suc+ ratios in sediments increased toward the mariculture areas with distance from the open sea at decreasing redox potentials. There is circumstantial evidence that suc− vibrios can be dispersed from mariculture areas to adjacent environments including coral reefs. An immediate human health risk by pathogenic Vibrio species is discounted, since milkfish guts contained mainly members of the Enterovibrio group. A representative isolate of these contained proteolytic and other virulence factors, but no genes encoding toxins characteristic of clinical Vibrio species.     

Spatiotemporal variability of hypoxia and eutrophication in Manila Bay,Philippines during the northeast and southwest monsoons

Hypoxia in Manila Bay, Philippines was previously reported during the northeast monsoon (dry season) in February 2010. In this study, four more field surveys of the same 31 stations were conducted in July 2010, August 2011 and 2012 (wet season, southwest monsoon), and February 2011 (dry season, northeast monsoon). During the wet season, bottom hypoxia spread northward towards the coast with dissolved oxygen (DO) ranging from 0.12 to 9.22 mg/L and the bay-wide average reaching 2.10 mg/L. Nutrient levels were elevated, especially near the bottom where dissolved inorganic nitrogen reached 22.3 μM (July 2010) and phosphorus reached 5.61 μM (August 2011). High nutrient concentrations often coincided with low near-bottom DO content. Our work builds on the preliminary assessment of hypoxia in Manila Bay, the importance of repeated temporal studies, and shows hypoxia to prevail significantly during the southwest monsoon (wet season) when increased freshwater discharge caused strong water column stratification.     

Behavior of Niobium, Tantalum and other high field strength elements in adakites and related lavas from The Philippines

Abstract Pliocene–Quaternary adakites and spatially and temporally associated niobium-enriched basalts (the latter thought to be derived by melting of slab melt-metasomatized mantle) from the Philippine island arcs have been selected for analysis of high field strength elements (HFSE). All these samples have nearly constant and chondritic Zr/Hf ratio (36.5) and slightly infrachondritic Nb/Ta ratio (14.7). We interpret adakitic magmas to be derived from the partial melting at approximately 900°C of subducted mid-ocean ridge basalts (MORB) crust, with rutile and/or ilmenite as residual minerals. Melting calculations show that, under these conditions, slab melts should have suprachondritic Nb/Ta ratios. The obvious discrepancy with our data is attributed to insufficient knowledge of rutile-melt partition coefficients for HFSE. Consequently, abnormal Nb/Ta or Zr/Hf ratios cannot be considered as potential markers of slab melting processes in island arcs.     

An analysis of livelihood projects and programs for fishing communities in the Philippines

Over the last 30 years, a range of different livelihoods have been provided and implemented in fishing and coastal communities in the Philippine with mixed success and sustainability by the fisher and household. This paper reports on an analysis of livelihood projects for fishing communities and households implemented in the Philippines and the identification of lessons learned and factors which can lead to an improved success and sustainability rate for livelihood projects and programs. The analysis identified primary factors that are critical to improving the success and sustainability rate of livelihood interventions.