The commodity boom economists have been predicting for months arrived in the June quarter as export prices increased by an historic level.

According to the Bureau of Statistics, the price of goods Australia exported surged by 16.1% in that quarter. That’s the largest increase recorded since at least 1974, when these figures were first tallied.

As the higher commodity prices miners negotiated with Asian buyers kicked in, prices for metal ores rose 43% and those for coal by 24.4% in the June quarter. These values were further boosted when the Australian dollar weakened by 2.4% in the quarter, boosting the value of commodities priced in U.S. dollars.

Import prices rose by 1.9%, as well, due to the lower dollar and higher prices for commodities Australia imports, such as fuel and food items. That was also a larger increase than economists expected and is likely to feed into the quarterly inflation figures, which print Wednesday and which are widely expected to influence the Reserve Bank’s rate-setting decision in early August.

Compared to twelve months ago, Australia’s export prices are now 7.1% higher and import prices are 5.2% lower.

Economists have been predicting a flood of wealth to flow into Australia from a new mining boom, principally through the terms of trade, which is the difference between export prices and import prices. An increase in the terms of trade feeds directly into an economy’s income, as imports become more affordable relative to an unchanged level of exports. For every 5% gain in a nation’s terms of trade, economists expect the growth rate to rise by a full percentage point prior to subtracting inflation.

Anthony Thompson, senior economist with Westpac, said the bank expects Australia’s terms of trade to rise 16% in the 2010–11 fiscal year, a return to the historic levels seen prior to the global financial crisis.