Gold commonly occurs in pyrite (FeS2) as "invisible" or refractory gold, as is the case at the giant Lihir (i.e., Ladolam) hybrid alkali-type gold deposit in Papua New Guinea. The Lihir gold deposit is also unique as it the exemplar of a telescoped ore deposit, whereby volcanic sector collapse led to superimposition of shallow-level gold-rich epithermal mineralization upon preexisting, but genetically related, porphyry-style alteration. While this superimposition led to a giant 56 Moz gold resource, it also created complications with regards to ore processing, specifically with regards to the difficulties in mineral processing of the refractory gold-rich pyritic ore.We have analyzed trace element zonation and composition of pyrite grains, using LA-ICP-MS imaging coupled with NaOCl etching, from a subset of spatially and paragenetically constrained pyrite-bearing samples from the Lienetz orebody. Pyrite grains belong to either porphyry-or epithermal-stages, or are composite pyrite grains with a multi-stage history. Trace element zonation and metal contents are unique to pyrite from each paragenetic event, providing insights into the nature of the mineralizing fluids. Early generations of coarse-grained pyrites that formed under higher temperature porphyry-style conditions have low trace element contents compared to epithermal-stage pyrites, except for Co, Ni and Se. Later generations of oscillatory zoned pyrites that formed under lower temperature epithermal conditions are comparatively enriched in trace elements such as As, Mo, Ag, Sb, Au and Tl. The composite pyrites are relatively coarse-grained and display textural and geochemical evidence of modification (i.e., dissolution and re-precipitation). They are interpreted to be porphyry-stage pyrite grains that have been overgrown by rims of delicate banded epithermal-style pyrite enriched in gold, arsenic and other trace elements.The composite pyrite grains are volumetrically dominant in the deep-seated anhydrite zone at Lienetz. Because gold is concentrated only along the rims of these pyrite grains, they can be subjected to a shorter period of oxidation and leaching to liberate most of their gold. This is in contrast for areas dominated by high-grade epithermal-stage mineralization where pyrite grains are arsenic-and gold-rich throughout, and thus require longer oxidation and processing time.Understanding gold deportment in telescoped deposits is therefore essential for optimising mineral processing and can impact significantly on the economics of mining these complex, hybrid ore deposits.

Without a doubt Hedican provides a necessary reevaluation of the events at Ipperwash in 1995 and the subsequent inquiry, however the book remains painfully muted up by its liberal sentiments. By reading through his objectivist positioning it become clear that this is a book aimed primarily at quelling settler fears of Indigenous resurgence by maintaining that a change in legislation is the solution to settler colonialism. While Hedican makes some mention of critical Indigenous scholarship his focus on the Canadian state denies a deeper anticolonial reading that would necessarily engage with Indigenous critique in a robust way. While Ipperwash remains one of the only books to analyze the topic at length its mode of analysis denies a critique of settler futurity ultimately limiting its usefulness for critical scholars of Canadian settler colonialism.

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The derivation of the mean temperature difference in heat exchangers is based on a number of assumptions or idealizations, the most important ones being that the heat transfer coefficient is constant throughout the exchanger; that the temperature of either fluid is constant over any cross section of its nominal path, that is, complete mixing, no stratification or bypassing; and that an additional assumption for shell and tube exchangers, which has not always been fully recognized, is that within one baffle crossing the shell fluid temperature change is small with respect to its overall change, (that is, number of baffles is large). In actual exchangers, any of the above assumptions are frequently subject to various degrees of invalidation. This paper examines the effects of deviating from the first two assumptions and presents a new solution to the third. KARL GARDNER SCOPEAs indicated by the title, this paper examines the magnitude of potential error in evaluation of the mean temperature difference (MTD) in heat exchangers caused by departure from a number of simplifying assumptions necessary for a straightforward solution of the MTD equations. Attention in this paper is confined to the three significant ones.1. The assumption that the overall coefficient is constant throughout the exchanger is most frequently violated, especially for fluids with steep viscosity characteristics and large temperature changes. Existing literature on this subject is scattered and confined to a few specific cases.2. Bypassing in heat exchangers occurs if the flow splits into several branches owing to unequal flow resistances. Each stream is exposed to different conditions of heat transfer, and the mixed exit temperature can be severely distorted against idealized assumptions. While this problem has been qualitatively realized for some ideal conditions, solutions for (or even awareness of) the potentially disastrous results in industrial applications have not been properly recognized.3. The consequences of the third assumption, that the number of baffles in a shell and tube exchanger is large, have never been analyzed before. The potential error is particularly apparent in a one shell pass-one tube pass exchanger, customarily considered as operating in counterflow. However, when only a few baffles are used, the flow in each baffle space is in cross flow, resulting in a possible severe MTD penalty. CONCLUSIONS AND SIGNIFICANCEWhile simplifying assumptions for solutions of the mean temperature difference (MTD) in heat exchangers are necessary for explicit solutions, most of the assumptions are violated in practical applications. This paper focuses on three assumptions considered the most frequent and most serious ones. For the first two assumptions, namely, change of the overall coefficient between hot and cold terminal temperatures and effects of fluid bypassing and unequal heat transfer, a critical review of the conditions leading to potential errors is presented. Remedial actions are recommended on a systematic basis as good as the...

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