Gold shot up more than 3% to its highest level since early June, good news for gold holders and a sign that investors are getting nervous about the US dollar and slowing growth.

• The US Treasury said it would double the size of its buyback support for long-dated government bonds, which caught markets off guard.
• That pushed long-term bond yields down sharply from near 19-year highs and weakened the dollar — both of which make gold more attractive.
• Gold pays no interest, so when bonds pay less, holding gold costs investors less.
• Talk of "stagflation" is building: growth is slowing while energy prices climb, and the Fed may look past the energy shock rather than raise rates again.
• Investors now put the odds at about two-in-three that the Fed leaves rates unchanged at its September meeting.

Outlook: Gold has broken back above a key technical level near $4,380 and, if it holds there, traders are likely to pile in further and push it toward $4,500.