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Peak Gold, Easier to Model than Peak Oil? - Part I
Jean Laherrère, The Oil Drum: Europe
Introduction

From Luis de Sousa on the Oil Drum:

In this first installment, an assessment of reserves and a production model is presented for each of major gold-producing countries in the world."

Introduction
Natural distributions (size versus rank) seem to follow the same fractal pattern (parabolic fractal) with galaxies, earthquakes, urban agglomerations and oil and gas reserves gathering in the same way (Laherrere 1996).

Mineral discoveries and production in sedimentary basins also seem to follow the same pattern, displaying several cycles trending towards an ultimate value. Production mimics discovery with a certain time lag, because what is produced needs to be discovered first.

However, production is limited both by above-ground and below-ground factors. The main below-ground limit is that the energy invested should be less than the energy returned, or EROI (Energy Return on Investment should be higher than 1). But EROI is very hard to estimate, except by converting expenditures for energy using assumed ratios...
(25 Nov 2009)
Very long article with 50 illustrations.

Could Peak Phosphate be Algal Diesel's Achilles' Heel?
Chris Rhodes, Energy Balance
The depletion of world phosphate reserves will impact on the production of biofuels, including the potential wide-scale generation of diesel from algae. The world population has risen to its present number of 6.7 billion in consequence of cheap fertilizers, pesticides and energy sources, particularly oil. Almost all modern farming has been engineered to depend on phosphate fertilizers, and those made from natural gas, e.g. ammonium nitrate, and on oil to run tractors etc. and to distribute the final produce. Worldwide production of phosphate has now peaked (in the US the peak came in the late 1980's), which lends fears as to how much food the world will be able to grow in the future, against a rising number of mouths to feed [1]. Consensus of analytical opinion is that we are close to the peak in world oil production too.

One proposed solution to the latter problem is to substitute oil-based fuels by biofuels, although this is not as straightforward as is often presented. In addition to the simple fact that growing fuel-crops must inevitably compete for limited arable land on which to grow food-crops, there are vital differences in the properties of biofuels, e.g. biodiesel and bioethanol, from conventional hydrocarbon fuels such as petrol and diesel, which will necessitate the adaptation of engine-designs to use them, for example in regard to viscosity at low temperatures, e.g. in planes flying in the frigidity of the troposphere. Raw ethanol needs to be burned in a specially adapted engine to recover more of its energy in terms of tank to wheels miles, otherwise it could deliver only about 70% of the "kick" of petrol, pound for pound.

In order to obviate the competition between fuel and food crops, it has been proposed to grow algae from which to make biodiesel. Some strains of algae can produce 50% of their weight of oil, which is transesterified into biodiesel in the same way that plant oils are. Compared to e.g. soy which might yield a tonne of diesel per hectare, or 8 tonnes from palm-oil, in excess of 100 tonnes (I shall assume 125 tonnes) per hectare is thought possible from algae, grown in ponds of equivalent area. Since the ponds can in principle be placed anywhere, there is no need to use arable land for them. Some algae grow well on salt-water too which avoids diverting increasingly precious freshwater from normal uses, as is the case for growing crops which require enormous quantities of freshwater.

The algae route sounds almost too good to be true. Having set-up these ponds, albeit on a large scale, i.e. they would need an area of 3,200 km^2 to produce 40 million tonnes of diesel, which is enough to match the UK's transportation demand for fuel if all vehicles were run on diesel-engines [the latter are more efficient in terms of tank to wheels miles by about 40% than petrol-fuelled spark-ignition engines], one could ideally leave them to absorb CO2 from the atmosphere (thus simultaneously solving another little problem) by photosynthesis, driven only by the flux of natural sunlight. The premise is basically true; however, for algae to grow, vital nutrients are also required, as a simple elemental analysis of dried algae will confirm. Phosphorus, though present in under 1% of that total mass, is one such vital ingredient, without which algal growth is negligible. I have used two different methods of calculation to estimate how much phosphate would be needed to grow enough algae, first to fuel the UK and then to fuel the world...
(6 April 2008)
Thanks to William Tamblyn for bringing Chris Rhodes' informative blog to my attention. An older article, but one that might help inform the current debate about algae? -KS

A Rock That Helps Out In a Hard Place
Sam Kornell, Miller-McCune
Folded into the mountains of northern Oman is a rare burst of peridotite rock. Viewed from above, its black-and-white striations make it look like a great scoop of marble fudge ice cream has been slathered across the earth.

In January 2008, a Columbia University doctoral student named Sam Krevor traveled to Oman to study the peridotite. For three showerless weeks he and a team of researchers surveyed, observed and catalogued the rock, camping under the stars and subsisting on an unlikely diet of cabbage and canned shellfish (nonperishable food items not being a staple of Omani grocery stores).

What were they looking for? The answer is as intriguing as it is unexpected. Peridotite, it turns out, absorbs carbon dioxide, and according to Krevor it potentially represents one of the greatest — if most bafflingly ignored — solutions to climate change in the world.

Originating deep in the earth, peridotite is a part of a family — "ultramafic rock" — that reacts naturally with CO2 to form solid minerals. Last May, Krevor was the lead author of a study identifying and mapping enough ultramafic rock in the United States to sequester an enormous amount of carbon dioxide. Taking into account various land-use constraints — private property, proximity to cities, national and state parks — he and his fellow researchers found storage potential for 500 years of the country's CO2 emissions.

..."It is very, very clear that we already have far more CO2 in the air than we can afford. That must be addressed, and we are not yet accepting, in public view, in public policy and in funding, how dire the situation is."

Insufficient research funding is the working scientist's perennial complaint. But considering how much money the federal government has already extended toward dubious climate solutions like biofuel, and considering how overwhelming the need to develop big solutions to climate change has become, it's difficult to understand why mineral sequestration — the potential merits of which are so impressive — hasn't garnered more attention...
(10 Nov 2009)