1. Long-term nitrogen (N) addition plots on an upland Cal/una vulgaris moor had been treated for more than ten years with 0,40, 80 and 120 kg N ha-1 yr- 1 • 2. Sampling of the soil solution from under the mor and the mineral gley horizons over an annual cycle revealed a high degree of retention of N, between 60 % and 80 % of ambient N inputs in the control, and rising to 90 % in response to higher inputs of the N treatments. 3. After passing through the mineral gley horizon, N was further retained, by 85 % of ambient N inputs in the control, and rising to 97 % in response to the highest N treatment. 4. There was some evidence of an inverse relation between ammonium and dissolved organic nitrogen (DON) under all N treatments. Microbial immobilisation and conversion to DON was compatible with the few significant effects on cation concentration, although calcium and calcium/aluminium ratios and pH were decreased by N treatment in the mineral gley horizon. 5. A budget revealed that the added N of the treatments had been allocated mainly to the canopy and litter at low inputs and increasingly to the mor, and to a lesser extent the gley horizon, with increasing N inputs. 6. In the system as a whole, 51 % of the entire system N was contained in the mor horizon, and with increasing inputs of added N, the whole system N accounted for 60 %, 80 % and 90 % of the added N in the low, middle and high N treatments respectively. 7. Nitrogen/phosphorus ratios in green tissue were decreased in response to increasing N inputs to levels indicative of N limitation, in spite of increases in phosphatase activity in the litter and mor layers. N uptake rates and mycorrhizal colonisation were not affected. 8. A moor management bum volatilised 90 % of the canopy N (amounting to 6 % of the total system N). Increases in the gain ofN in the gley horizon after the bum decreased with increasing N treatment, an indication of increasing N saturation in this layer and confirmed by increases in N leaching in response to higher N inputs. The same response was observed without significance in the mor layer owing to greater variance in the data. 9. Rates of net mineralisation and DON production in the litter layer increased with N inputs in both field and laboratory incubations, but net nitrification rate only showed N treatment-related increases in the laboratory incubation. Threshold values of litter % N and C/N ratios determined the onset of these processes, as well as N treatment-related increases in rates of potential denitrification. 10. Bryophyte cover under the Calluna canopy, density of the canopy, light transmission through the canopy and N inputs were all related, either negatively or positively (see chapter 5), but only in mature/degenerate plants. In "new' plots containing younger, building-phase Calluna, the addition of phosphorus raised the competitive ability of bryophytes above that of Calluna, particularly at lower inputs of N.

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Two aspects of gold mineralisation in the Caledonides of the British Isles have been investigated: gold-telluride mineralisation at Clogau Mine, North Wales; and placer gold mineralisation in the Southern Uplands, Scotland. The primary ore assemblage at Clogau Mine is pyrite, arsenopyrite, cobaltite, pyrrhotine, chalcopyrite, galena, tellurbismuth, tetradymite, altaite, hessite, native gold, wehrlite, hedleyite, native bismuth, bismuthunite and various sulphosalts. The generalised paragenesis is early Fe, Co, Cu, As and S species, and later minerals of Pb, Bi, Ag, Au, Te, Sb. Electron probe micro-analysis (EPMA) of complex telluride-sulphide intergrowths suggests that these intergrowths formed by co-crystallisation/replacement processes and not exsolution. Minor element chemical variation, in the sulphides and tellurides, indicates that antimony and cadmium are preferentially partitioned into telluride minerals. Mineral stability diagrams suggest that during gold deposition log bf aTe2 was between -7.9 and -9.7 and log bf aS2 between -12.4 and -13.8. Co-existing mineral assemblages indicate that the final stages of telluride mineralisation were between c. 250 - 275oC. It is suggested that the high-grade telluride ore shoot was the result of remobilisation of Au, Bi, Ag and Te from low grade mineralisation elsewhere within the vein system, and that gold deposition was brought about by destabilisation of gold chloride complexes by interaction with graphite, sulphides and tellurbismuth. Scanning electron microscopy of planer gold grains from the Southern Uplands, Scotland, indicates that detailed studies on the morphology of placer gold can be used to elucidate the history of gold in the placer environment. In total 18 different morphological characteristics were identified. These were divided on an empirical basis, using the relative degree of mechanical attrition, into proximal and distal characteristics. One morphological characteristic (a porous/spongy surface at high magnification) is considered to be chemical in origin and represent the growth of `new' gold in the placer environment. The geographical distribution of morphological characteristics has been examined and suggests that proximal placer gold is spatially associated with the Loch Doon, Cairsphairn and Fleet granitoids. Quantitative EPMA of the placer gold reveals two compositional populations of placer gold. Examination of the geographical distribution of fineness suggests a loose spatial association between granitoids and low fineness placer gold. Also identified was chemically heterogeneous placer gold. EPMA studies of these heterogeneities allowed estimation of annealing history limits, which suggest that the heterogeneities formed between 150 and 235oC. It is concluded, on the basis of relationships between morphology and composition, that there are two types of placer gold in the Southern Uplands: (i) placer gold which is directly inherited from a hypogene source probably spatially associated with granitoids; and (ii) placer gold that has formed during supergene processes.

Mineralisation in the South Pennine MVT orefield (225km2) has resulted from the combined effects of basement structure, stress history and basin evolution during the Carboniferous. NW-SE-trending Caledonian thrusts in the basement beneath North Derbyshire were reactivated as normal growth faults during limestone sedimentation in the Dinantian. on a regional scale, a major low-angle detachment, dipping NE away from St. George's Land (20km to the SW of North Derbyshire), controlled basin development as far as the Askern-Spital High (100km to the NE). The North Derbyshire shelf developed on the up-dip crest of a NE-tilted half-graben, in the hanging wall of this detachment, directly above the zone of mantle upwelling. A similar structure also evolved in the Rotherham area, some 40km to the NE, where, it is inferred, another orefield exists in the subsurface. In North Derbyshire, the end of the Dinantian was a period of uplift and erosion. In the NE part of the shelf, dextral wrench faults developed above ENE-WSW-trending basement fractures. At the start of the Namurian the direction of extension rotated to NW-SE and by the end of the Westphalian the limestone was buried to a depth of about 2km (~130°C) due to the combined effects of thermal sag and sediment compaction. Mineralisation began in the early Stephanian, associated with a period of N-S extension. Fractures in the limestone formed during earlier tectonic events began to dilate, thus allowing inflow of acidic F-Ba-Pb-zn-S-enriched fluid expelled from overlying Namurian shales. This was replenished by meteoric water migrating westwards down-dip from the uplifted Askern-Spital-Nocton-Grantham High. Ore deposition occurred within the limestone as a result of increasing pH, Ca 2+ and SO42 in the orefluid due to wallrock dissolution and fluid mixing. Mineralisation probably continues in the subsurface for some distance to the SE of the South Pennine orefield in shallow-water limestones with a similar structural aspect to those exposed in North Derbyshire.

The Rosita Hills volcanic centre is an alkali-calcic mid-Tertiary caldera complex overlying ortho- and paragneissic basement on the eastern margin of the Wet Mountains graben in southcentral Colorado. There were two mineralising events at the Rosita centre. Au, Ag and base metal mineralisation occurred in a phreatomagmatic breccia pipe at the northern margin of the complex. Later, Ag and base metal mineralisation occurred in veins in the centre of the complex. Mapping, petrological and XRD studies outline 4 alteration facies related to hydrothermal activity at the centre. Propylitic/argillic, K-feldspar-sericitic, advanced argillic and silicic alteration assemblages are recognised. The areas of most intense alteration are controlled by the dominant structural trends within the caldera. Sub-volcanic magma movement is postulated as the dominant cause of the fracture patterns. A lithogeochemical grid survey for Au, Ag, Sr, Rb, Cu, Pb, Zn and Mn across areas of hydrothermal alteration reveal complex patterns indicative of multi-stage hydrothermal activity. District-wide Sr, Zn and Mn depletions are related to the propylitic/argillic alteration. Au, Ag, Rb and Cu enhancements are related to the K-feldspar-sericite alteration. Late stage advanced argillic alteration modified the trace element dispersion patterns by leaching previously formed enhancements. Stable isotope studies (O and H) of whole rock and mineral separate (quartz and sericite) samples from veins and hydrothermal eruption breccias show that the hydrothermal fluid had both meteoric and magmatic components. δD values from whole rock samples show a crudely concentric pattern centring on areas of sericitic and advanced argillic alteration in the middle of the lithogeochemical grid. Fluid inclusion data from vein gangue minerals (quartz, baryte and sphalerite) and from silicified rock in the advanced argillic alteration zone again show that the hydrothermal fluid had more than one component fluid. A highly saline, high temperature fluid occurs in quartz associated with base metal mineralisation. Less saline inclusions occur in the upper parts of the system in the silicic alteration. The data indicate that mixing of these two end-member fluids precipitated the vein mineralisation. The source of metals in the Bassick breccia pipe orebody was a highly differentiated magma body underlying the breccia pipe. Incipient ring faulting probably controlled the emplacement of the magma. Other similar breccia pipes in Colorado are postulated as overlying Cu-Mo porphyry mineralisation. The source of the metals in the Rosita vein orebodies was the volcanic host rocks (and the Precambrian basement?). The Rosita Hills vein mineralisation shows features typical of adularia-sericite systems in the western United States. The Au:Ag ratio in these deposits can be related to the origins of the crust underlying the deposits.