Explain why the scarcity of high-grade copper ores necessitates the development of new extraction methods.

The scarcity of high-grade copper ores means that traditional mining methods are becoming less viable due to lower yields and higher costs. As these ores are depleted, new extraction methods, such as bioleaching and phytomining, are needed to efficiently obtain copper from lower-grade ores and reduce environmental impact.

A strong answer should directly address the approved learning objective to explain that metal ores are limited resources. This question belongs to Alternative methods of extracting metals within Using the Earth's resources and obtaining potable water, so the response should use that exact curriculum context rather than a generic statement. The answer is correct when it names the key idea, explains the link to limited resources, and keeps the wording specific to AQA GCSE revision.