Nozick adds that when a person mixes his own resources, such as labor, into a natural resource, a conversion of public, natural property turns in private property in the process. This conversion forms the basis of Nozick’s initial acquisition theory, a first step in his justice by just steps basis for the Entitlement State in Anarchy, State and Utopia.
A 2010 article about land “reform” in Zimbabwe reminded me of Nozick’s writing on the subject: http://news.bbc.co.uk/2/hi/africa/8617684.stm
Nozick is sometimes criticized for the practicality of his ideas, particularity the enforceability of the Lockean Proviso. How far back should the state go to enforce ownership rights accruing to the “original” peoples who mixed their labor with land? What if the results are disastrous?